Network Working Group Request for Comments: 3588 Category: Standards Track

Diameter Base Protocol Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2003). Abstract The Diameter base protocol is intended to provide an Authentication, Authorization and Accounting (AAA) framework for applications such as network access or IP mobility. Diameter is also intended to work in both local Authentication, Authorization & Accounting and roaming situations. This document specifies the message format, transport, error reporting, accounting and security services to be used by all Diameter applications. The Diameter base application needs to be supported by all Diameter implementations. Conventions Used In This Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119 [KEYWORD]. All Rights Reserved.

.. and TLS support is optional. These include: Failover [RADIUS] does not define failover mechanisms..... Transmission-level security [RADIUS] defines an application-layer authentication and integrity scheme that is required only for use with Response packets........ and as a result.. Over time. failover behavior differs between implementations.... with the growth of the Internet and the introduction of new access technologies. routers and network access servers (NAS) have increased in complexity and density.
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... While [RFC3162] defines the use of IPsec with RADIUS.. including wireless...... and defines failover algorithms and the associated state machine...and inter-domain AAA deployments........ rather than within the protocol itself. DSL... putting new demands on AAA protocols.... Since within [IKE] authentication occurs only within Phase 1 prior to the establishment of IPsec SAs in Phase 2.. This limits the usefulness of IPsec in inter-domain AAA applications (such as roaming) where it may be desirable to define a distinct certificate hierarchy for use in a AAA deployment.... [RADIUS] does not provide support for per-packet confidentiality.. and enable both intra.. [RADACCT] assumes that replay protection is provided by the backend billing server.. IPsec support is mandatory in Diameter.. Authorization and Accounting (AAA) protocols such as TACACS [TACACS] and RADIUS [RADIUS] were initially deployed to provide dial-up PPP [PPP] and terminal server access. 146 Full Copyright Statement. 145 Authors’ Addresses. Mobile IP and Ethernet.. This is described in Section 5..RFC 3588
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Appendix D..... support for IPsec is not required. In order to provide universal support for transmission-level security....... Security is discussed in Section 13........
Calhoun...5 and [AAATRANS]. et al..... In order to provide well defined failover behavior.. Introduction Authentication..... Diameter supports application-layer acknowledgements... Network access requirements for AAA protocols are summarized in [AAAREQ].. it is typically not possible to define separate trust or authorization schemes for each application. Intellectual Property Statement......... In accounting... While attribute-hiding is supported....... use is only required during Extensible Authentication Protocol (EAP) sessions. 147 1........... While [RADEXT] defines an additional authentication and integrity mechanism.

including Proxies. In order to provide well defined transport behavior. these capabilities are supported. Agent support [RADIUS] does not provide for explicit support for agents. enables Diameter support to be added to legacy networks.8. where packet loss may translate directly into revenue loss. Server-initiated messages While RADIUS server-initiated messages are defined in [DYNAUTH].RFC 3588
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Reliable transport RADIUS runs over UDP. it is expected that Diameter will be deployed within new network devices. it varies between implementations. Redirects and Relays. as a result. considerable effort has been expended in enabling backward compatibility with RADIUS. Diameter defines agent behavior explicitly. Auditability RADIUS does not define data-object security mechanisms. Combined with lack of support for capabilities negotiation. Transition support While Diameter does not share a common protocol data unit (PDU) with RADIUS. and does not define retransmission behavior. and is described in Section 8.
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. SCTP) as defined in [AAATRANS]. While implementation of data object security is not mandatory within Diameter. et al. This capability. untrusted proxies may modify attributes or even packet headers without being detected. As described in [ACCMGMT]. This makes it difficult to implement features such as unsolicited disconnect or reauthentication/reauthorization on demand across a heterogeneous deployment. and as a result. reliability varies between implementations. this is described in Section 2. this is a major issue in accounting. this makes it very difficult to determine what occurred in the event of a dispute. Since the expected behavior is not defined. by addition of a gateway or server speaking both RADIUS and Diameter. and are described in [AAACMS]. so that the two protocols may be deployed in the same network. Diameter runs over reliable transport mechanisms (TCP. support is optional. Initially. Support for server-initiated messages is mandatory in Diameter. as well as within gateways enabling communication between legacy RADIUS devices and Diameter agents.
Calhoun. described in [NASREQ].

which can result in major security vulnerabilities if the Request Authenticator is not globally and temporally unique as required in [RADIUS]. However.3). capability negotiation. As a result. it remains feasible to implement
Calhoun. or in some cases. while Diameter is a considerably more sophisticated protocol than RADIUS. along with the corresponding shared secrets. This results in a large administrative burden. Through DNS. and documented existing implementations (and imitations) of RADIUS-based roaming [PROXYCHAIN].7 and 6). auditability [AAACMS]. facilitating roaming between providers. and mandatory/non-mandatory attribute-value pairs (AVPs) (Section 4. Derivation of dynamic session keys is enabled via transmission-level security. the capabilities of Network Access Server (NAS) devices have increased substantially. Diameter addresses these limitations and provides for secure and scalable roaming. Diameter also provides support for the following: Capability negotiation RADIUS does not support error messages. Diameter enables dynamic discovery of peers. In the decade since AAA protocols were first introduced. and transmission-layer security (Section 13) features. [PROXYCHAIN] introduced the concept of proxy chaining via an intermediate server.1). detailed roaming requirements [ROAMCRIT]. As a result.RFC 3588
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In addition to addressing the above requirements. By providing explicit support for inter-domain roaming and message routing (Sections 2. since RADIUS does not provide explicit support for proxies. they may not be able to successfully negotiate a mutually acceptable service. even be aware of what service has been implemented. Since RADIUS clients and servers are not aware of each other’s capabilities. Roaming support The ROAMOPS WG provided a survey of roaming implementations [ROAMREV]. Diameter includes support for error handling (Section 7). and creates the temptation to reuse the RADIUS shared secret. and lacks auditability and transmission-level security features. or a mandatory/non-mandatory flag for attributes. Peer discovery and configuration RADIUS implementations typically require that the name or address of servers or clients be manually configured. defined the Network Access Identifier (NAI) [NAI].
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. et al. RADIUSbased roaming is vulnerable to attack from external parties as well as susceptible to fraud perpetrated by the roaming partners themselves. In order to improve scalability. it is not suitable for wide-scale deployment on the Internet [PROXYCHAIN]. capability negotiation (Section 5.

Basic services necessary for applications. The base protocol may be used by itself for accounting purposes only. AVPs are used by the base Diameter protocol to support the following required features: Transporting of user authentication information. via the addition of new commands or AVPs. et al. A truly generic AAA protocol used by many applications might provide functionality not provided by Diameter. AVPs may be added arbitrarily to Diameter messages.
Calhoun. Transporting of service specific authorization information.
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The Diameter base protocol provides the minimum requirements needed for a AAA protocol. or network access [NASREQ]. as required by [AAAREQ]. At this time the focus of Diameter is network access and accounting applications.
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. Diameter Protocol
The Diameter base protocol provides the following facilities: Delivery of AVPs (attribute value pairs) Capabilities negotiation Error notification Extensibility. which MAY be used for accounting purposes. through addition of new commands and AVPs (required in [AAAREQ]). such as Mobile IPv4 [DIAMMIP]. Some of these AVP values are used by the Diameter protocol itself. given improvements in processor speeds and the widespread availability of embedded IPsec and TLS implementations.1. between client and servers. it is imperative that the designers of new applications understand their requirements before using Diameter. proxying and redirecting of Diameter messages through a server hierarchy. or it may be used with a Diameter application.RFC 3588
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within embedded devices. etc. while others deliver data associated with particular applications that employ Diameter. It is also possible for the base protocol to be extended for use in new applications. for the purposes of enabling the Diameter server to authenticate the user. allowing the peers to decide whether a user’s access request should be granted. so long as the required AVPs are included and AVPs that are explicitly excluded are not included. 1. Exchanging resource usage information. Therefore. capacity planning. such as handling of user sessions or accounting
All data delivered by the protocol is in the form of an AVP. Relaying.

1. and accounting services for the user. 1. redirects and relay agents. authorization. such as a Network Access Server (NAS) or a Foreign Agent (FA). agents include proxies. Authorization and Accounting. which includes support for accounting. Consideration was given for servers that need to perform protocol conversion between Diameter and RADIUS.1. Diameter is a peerto-peer protocol. A Diameter server performs authentication and/or authorization of the user. such as a request to abort service to a particular user.4 for more information on Diameter applications.
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. A Diameter client generates Diameter messages to request authentication. The Transport Profile document [AAATRANS] discusses transport layer issues that arise with AAA protocols and recommendations on how to overcome these issues. this document defines the base protocol specification for AAA. This document also defines the Diameter failover algorithm and state machine. In this document. A Diameter agent is a node that does not authenticate and/or authorize messages locally. The NASREQ [NASREQ] application defines a Diameter Application that allows a Diameter server to be used in a PPP/SLIP Dial-Up and Terminal Server Access environment.RFC 3588
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See Section 2. In that sense. et al. Transport Profile [AAATRANS] and applications: Mobile IPv4 [DIAMMIP]. The Mobile IPv4 [DIAMMIP] application defines a Diameter application that allows a Diameter server to perform AAA functions for Mobile IPv4 services to a mobile node. Any node can initiate a request. Description of the Document Set
Currently. and NASREQ [NASREQ]. the Diameter specification consists of a base specification (this document).
Calhoun. a Diameter Client is a device at the edge of the network that performs access control. In summary. A Diameter node MAY act as an agent for certain requests while acting as a server for others. The Diameter protocol also supports server-initiated messages. The Mobile IPv4 and the NASREQ documents describe applications that use this base specification for Authentication.

an application may require a new value to communicate some service-specific information.2.
Calhoun.3. In order to create a new AVP. including: Defining new AVP values Creating new AVPs Creating new authentication/authorization applications Creating new accounting applications Application authentication procedures
Reuse of existing AVP values.2. 1. it is recommended that a Grouped AVP be used (see Section 4.
Approach to Extensibility
The Diameter protocol is designed to be extensible. For AVPs of type Enumerated. using several mechanisms.
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.2. et al. Creating New Authentication Applications
Every Diameter application specification MUST have an IANA assigned Application Identifier (see Section 2. and multiple "groups" are possible in a given command. It is expected that command codes are reused. as opposed to creating new AVPs.1). Defining New AVP Values
New applications should attempt to reuse AVPs defined in existing applications when possible. In order to allocate a new AVP value. The request MUST include the commands that would make use of the AVP. new AVP being defined MUST use one of the data types listed in Section 4. 1. with a specification for the AVP.4) or a vendor specific Application Identifier. AVPs and Diameter applications are strongly recommended.RFC 3588
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1.
In the event that a logical grouping of AVPs is necessary. Creating New AVPs The
When no existing AVP can be used. along with an explanation of the new AVP value. a new AVP should be created. Reuse simplifies standardization and implementation and avoids potential interoperability issues.2.2. a request MUST be sent to IANA [IANA].2. new command codes can only be created by IETF Consensus (see Section 11. IANA considerations for Diameter are discussed in Section 11.1.2.4). 1. a request MUST be sent to IANA.

et al. Diameter applications MUST define one Command Code.
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.g. addition of EAP methods does not require the creation of a new authentication application. The expected AVPs MUST be defined in an ABNF [ABNF] grammar (see Section 3. If the Diameter application has accounting requirements. it may be desirable to create a new Diameter application. Major changes to an application include: Adding new AVPs to the command. it MUST also specify the AVPs that are to be present in the Diameter Accounting messages (see Section 9.4. but new application bar has a command that requires two round trips to complete). Since a new EAP authentication method can be supported within Diameter without requiring new AVPs. When possible. does not imply that a new accounting application id is required. including vendor-specific AVPs without needing to define a new application.3). but do not need to define new command codes. An implementation MAY add arbitrary non-mandatory AVPs (AVPs with the "M" bit not set) to any command defined in an
Calhoun. just because a new authentication application id is required. In order to justify allocation of a new application identifier. Requiring a command that has a different number of round trips to satisfy a request (e. or add new mandatory AVPs to the ABNF. However. Creating New Accounting Applications
There are services that only require Diameter accounting.2. Please refer to Section 11. An implementation MAY add arbitrary non-mandatory AVPs to any command defined in an application.1 for details..2). application foo has a command that requires one round trip. which have the "M" bit set.1.
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Creation of a new application should be viewed as a last resort. in order to avoid defining multiple AVPs that carry similar information.RFC 3588
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Should a new Diameter usage scenario find itself unable to fit within an existing application without requiring major changes to the specification. Such services need to define the AVPs carried in the Accounting-Request (ACR)/ Accounting-Answer (ACA) messages. 1. Adding support for an authentication method requiring definition of new AVPs for use with the application. a new Diameter application SHOULD reuse existing Diameter AVPs.

1 for details. a new Diameter accounting application SHOULD attempt to reuse existing AVPs. new commands or additional mechanisms (e.1.4) or a vendor specific Application Identifier. The creation of a new accounting application should be viewed as a last resort and MUST NOT be used unless a new command or additional mechanisms (e.4) MUST be used in ACR/ACA commands. A DIAMETER base accounting implementation MUST be configurable to advertise supported accounting applications in order to prevent the accounting server from accepting accounting requests for unbillable services. Basic accounting support is sufficient to handle any application that uses the ACR/ACA commands defined in this document. or new mandatory AVPs are added to the ABNF. application defined state machine) is defined within the application. billing server) or the accounting server itself MUST understand the AVP in order to compute a correct bill. Application Identifiers are still required for Diameter capability exchange.e. authentication/authorization commands). in order to avoid defining multiple AVPs that carry similar information.RFC 3588
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application. setting the "M" bit implies that a backend server (e.g. including vendor-specific AVPs. regardless of whether it is required or optional within the ABNF for the accounting application. application defined state machine). then the base protocol defined standard accounting application Id (Section 2. Please refer to Section 11. The combination of the home domain and the accounting application Id can be used in order to route the request to the appropriate accounting server. Every Diameter accounting application specification MUST have an IANA assigned Application Identifier (see Section 2. When possible.. A mandatory AVP is defined as one which has the "M" bit set when sent within an accounting command.. If the base accounting is used without any mandatory AVPs. without needing to define a new accounting application. when the AVP is included within an accounting command.
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. it MUST NOT have the "M" bit set.g. even if the "M" bit is set when the same AVP is used within other Diameter commands (i.. Within an accounting command.. If the AVP is not relevant to the billing process. as long as no new mandatory AVPs are added. Every Diameter implementation MUST support accounting.
Calhoun. et al.g.

et al. Broker A broker A broker operated a broker agents. 1. When possible.g.RFC 3588
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1.
Application Authentication Procedures
When possible. This MAY require that new AVP values be assigned to represent the new authentication transform. applications SHOULD be designed such that new authentication methods MAY be added without requiring changes to the application. proxy or redirect agent. Authorization The act of determining whether a requesting entity (subject) will be allowed access to a resource (object). billing or cost allocation. or any other scheme that produces similar results. AAA Authentication. is either a relay. routing information) as well as authentication. such as Extensible Authentication Protocol [EAP].5. Terminology
is a business term commonly used in AAA infrastructures. may either choose to deploy relay agents or proxy
Calhoun. Accounting Record An accounting record represents a summary of the resource consumption of a user over the entire session. auditing. Accounting The act of collecting information on resource usage for the purpose of capacity planning. An AVP includes a header and is used to encapsulate protocol-specific data (e. authentication frameworks. SHOULD be used. AVP The Diameter protocol consists of a header followed by one or more Attribute-Value-Pairs (AVPs). Authentication The act of verifying the identity of an entity (subject).2.3.. Accounting servers creating the accounting record may do so by processing interim accounting events or accounting events from several devices serving the same user.
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. and MAY be by roaming consortiums. authorization or accounting information. Depending on the business model. Authorization and Accounting.

this hop-by-hop security does not protect the entire Diameter user session. redirect or translation services. a Diameter Server MUST support Diameter applications in addition to the base protocol. its very nature. Diameter Node A Diameter node is a host process that implements the Diameter protocol. Agent or Server. Home Realm A Home Realm is the administrative domain with which the user maintains an account relationship. proxy. Diameter Peer A Diameter Peer is a Diameter Node to which a given Diameter Node has a direct transport connection. et al. or security across a transport connection. This security protects the entire Diameter communications path from the originating Diameter node to the terminating Diameter node. End-to-end security is security between two Diameter nodes. Home Server See Diameter Server. When relays or proxy are involved. and acts either as a Client. An example of a Diameter client is a Network Access Server (NAS) or a Foreign Agent (FA). possibly communicating through Diameter Agents. End-to-End Security TLS and IPsec provide hop-by-hop security. authorization and accounting requests for a particular realm. Diameter Security Exchange A Diameter Security Exchange is a process through which two Diameter nodes establish end-to-end security. Diameter Server A Diameter Server is one that handles authentication.RFC 3588
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Diameter Agent A Diameter Agent is a Diameter node that provides either relay. Diameter Client A Diameter Client is a device at the edge of the network that performs access control.
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.
Calhoun.
By
Downstream Downstream is used to identify the direction of a particular Diameter message from the home server towards the access device.

This is typically accomplished by tracking the state of NAS devices. while the realm is used for message routing purposes. Local Realm A local realm is the administrative domain providing services to a user. Diameter makes use of the realm. NAI realm names are required to be unique. The identity is used to identify the user during authentication and/or authorization.RFC 3588
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Interim accounting An interim accounting message provides a snapshot of usage during a user’s session. or whether they must be routed or redirected. An would be a Multi-link PPP bundle. Realm The string in the NAI that immediately follows the ’@’ character. While proxies typically do not respond to client Requests prior to receiving a Response from the server. proxies need to understand the semantics of the messages passing through them.
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. et al. also loosely referred to as domain. and are piggybacked on the administration of the DNS namespace. by using the Acct-Multi-Session-Id. proxies make policy decisions relating to resource usage and provisioning.
Calhoun. or NAI [NAI].
a logical linking of several sessions. and may not support all Diameter applications. In RADIUS. to determine whether messages can be satisfied locally. Each a session while the entire bundle would
Network Access Identifier The Network Access Identifier. while being a home realm for others. An administrative domain MAY act as a local realm for certain users. Proxy Agent or Proxy In addition to forwarding requests and responses. they may originate Reject messages in cases where policies are violated. realm names are not necessarily piggybacked on the DNS namespace but may be independent of it. is used in the Diameter protocol to extract a user’s identity and realm. Multi-session A multi-session represents Multi-sessions are tracked example of a multi-session leg of the bundle would be be a multi-session. As a result. It is typically implemented in order to provide for partial accounting of a user’s session in the case of a device reboot or other network problem prevents the reception of a session summary message or session record.

Security Association A security association is an association between two endpoints in a Diameter session which allows the endpoints to communicate with integrity and confidentially. redirect agents refer clients to servers and allow them to communicate directly.RFC 3588
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Real-time Accounting Real-time accounting involves the processing of information on resource usage within a defined time window. et al. they do not alter any AVPs transiting between client and server.
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. Relay Agent or Relay Relays forward requests and responses based on routing-related AVPs and realm routing table entries. Each application SHOULD provide guidelines as to when a session begins and ends. and relationships between an ISP and a roaming consortium. All Diameter packets with the same Session-Identifier are considered to be part of the same session. Roaming Relationships Roaming relationships include relationships between companies and ISPs. they do not examine or alter non-routing AVPs. Since relays do not make policy decisions. do not need to understand the semantics of messages or non-routing AVPs. As with proxy agents. relays never originate messages. Time constraints are typically imposed in order to limit financial risk. redirect agents do not keep state with respect to sessions or NAS resources. As a result. Since redirect agents do not sit in the forwarding path. although they may be configured only to redirect messages of certain types. Session A session is a related progression of events devoted to a particular activity. while acting as relay or proxy agents for other types. Since relays make decisions based on information in routing AVPs and realm forwarding tables they do not keep state on NAS resource usage or sessions in progress.
Calhoun. even in the presence of relays and/or proxies. relationships among peer ISPs within a roaming consortium. Redirect agents do not originate messages and are capable of handling any message type. and are capable of handling any Diameter application or message type. Redirect Agent Rather than forwarding requests and responses between clients and servers.

Calhoun.. Sub-session A sub-session represents a distinct service (e. Upstream Upstream is used to identify the direction of a particular Diameter message from the access device towards the home server. QoS or data characteristics) provided to a given session. the field is replaced with a locally unique identifier. the Hop-by-Hop identifier is saved. The request’s state is released upon receipt of the answer. by keeping track of all authorized active sessions. but for use in authentication and authorization it is always extended for a particular application. These changes in sessions are tracked with the Accounting-Sub-Session-Id. which is used for failover purposes. These services may happen concurrently (e.
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. or by expiration. Transport Connection A transport connection is a TCP or SCTP connection existing directly between two Diameter peers. which is restored to its original value when the corresponding answer is received.g. 2.RFC 3588
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Session state A stateful agent is one that maintains session state information. Two Diameter applications are defined by companion documents: NASREQ [NASREQ]. et al.g. otherwise known as a Peerto-Peer Connection. and its state is considered active either until it is notified otherwise. Each authorized session is bound to a particular service. simultaneous voice and data transfer during the same session) or serially. Translation Agent A translation agent is a stateful Diameter node that performs protocol translation between Diameter and another AAA protocol. Transaction state The Diameter protocol requires that agents maintain transaction state. User The entity requesting or using some resource. Protocol Overview The base Diameter protocol may be used by itself for accounting applications. A stateless agent is one that only maintains transaction state. such as RADIUS.. in support of which a Diameter client has generated a request. Transaction state implies that upon forwarding a request.

Additional Diameter applications MAY be defined in the future (see Section 11.. In addition.RFC 3588
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Mobile IPv4 [DIAMMIP]. In addition. by definition. and all Diameter applications. MUST be referred to as "Diameter X Client" where X is the application which it supports. Communication between Diameter peers begins with one peer sending a message to another Diameter peer. The base protocol also defines certain rules that apply to all exchanges of messages between Diameter nodes. and MUST transparently support the Diameter base protocol. In addition. Diameter Servers MUST support the base protocol. and not a "Diameter Client".
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. they MUST fully support each Diameter application that is needed to implement the intended service. they MUST fully support each Diameter application that is needed to implement the client’s service. A Diameter Server that does not support both NASREQ and Mobile IPv4. Diameter proxies MUST support the base protocol. and not a "Diameter Proxy".3). e. e. which includes accounting.g. The base Diameter protocol concerns itself with capabilities negotiation. they MUST fully support each Diameter application that is needed to implement proxied services.g.g. NASREQ and/or Mobile IPv4. MUST be referred to as "Diameter X Server" where X is the application which it supports. et al. or reject it by returning an answer message with the Result-Code AVP
Calhoun. NASREQ and/or Mobile IPv4. protocol transparent.. The set of AVPs included in the message is determined by a particular Diameter application. Diameter Clients MUST support the base protocol. e. The initial request for authentication and/or authorization of a user would include the Session-Id. A Diameter proxy which does not support also both NASREQ and Mobile IPv4. One AVP that is included to reference a user’s session is the Session-Id. A Diameter Client that does not support both NASREQ and Mobile IPv4. which includes accounting.. NASREQ and/or Mobile IPv4. These applications are introduced in this document but specified elsewhere. The Session-Id is then used in all subsequent messages to identify the user’s session (see Section 8 for more information). and not a "Diameter Server". which includes accounting. The communicating party may accept the request. Diameter Relays and redirect agents are. MUST be referred to as "Diameter X Proxy" where X is the application which it supports. which includes accounting. how messages are sent and how peers may eventually be abandoned.

1. and MUST be prepared to receive connections on port 3868.
Calhoun. Session-TerminationAnswer. SCTP SHOULD be tried first. When no transport connection exists with a peer. Transport
Transport profile is defined in [AAATRANS].
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. while agents and servers MUST support both. such as when a peer has terminated the transport connection stating that it does not wish to communicate. expiration of authorized service time in the Session-Timeout AVP. 2. The base Diameter protocol is run on port 3868 of both TCP [TCP] and SCTP [SCTP] transport protocols. followed by TCP. A Diameter node MAY initiate connections from a source port other than the one that it declares it accepts incoming connections on. whose recommended value is 30 seconds. When connecting to a peer and either zero or more transports are specified. The specific behavior of the Diameter server or client receiving a request depends on the Diameter application employed. and according to rules established in a particular Diameter application. A given Diameter instance of the peer state machine MUST NOT use more than one transport connection to communicate with a given peer.2 for more information on peer discovery. This behavior is handled via the Tc timer.RFC 3588
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set to indicate an error occurred. There are certain exceptions to this rule. unless multiple instances exist on the peer in which case a separate connection per process is allowed. subject to security policy on trusting such messages. et al. Diameter implementations SHOULD also be able to interpret a reset from the transport and timed-out connection attempts. an attempt to connect SHOULD be periodically made. Diameter clients MUST support either TCP or SCTP. Future versions of this specification MAY mandate that clients support SCTP. Diameter implementations SHOULD be able to interpret ICMP protocol port unreachable messages as explicit indications that the server is not reachable. See Section 5. Session state (associated with a Session-Id) MUST be freed upon receipt of the Session-Termination-Request.

For a given application.3). the stream is compromised and cannot be recovered. 2.
Calhoun. Securing Diameter Messages
Diameter clients. such as Network Access Servers (NASes) and Mobility Agents MUST support IP Security [SECARCH]. This also eases the requirements on the NAS support certificates.1 and 13. The transport connection MUST be closed using a RESET call (send a TCP RST bit) or an SCTP ABORT message (graceful closure is compromised). and MAY support TLS [TLS]. 2. et al. advertising support of an application implies that the sender supports all command codes. such as using pre-shared keys between a local AAA proxy. It is also suggested that inter-domain would primarily use TLS. To prevent blocking: All Diameter nodes SHOULD utilize all SCTP streams available to the association to prevent head-of-the-line blocking.3. 2. Please refer to Section 11. Diameter Application Compliance and in NAS a to traffic details
Application Identifiers are advertised during the capabilities exchange phase (see Section 5.1.2. For interoperability: All Diameter nodes MUST be prepared to receive Diameter messages on any SCTP stream in the association. and the AVPs specified in the associated ABNFs.2 for more on IPsec and TLS usage.1.1. It is suggested that IPsec can be used primarily at the edges intra-domain traffic.1 for details. 2.RFC 3588
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If Diameter receives data up from TCP that cannot be parsed or identified as a Diameter error made by the peer. including vendor-specific AVPs. The Diameter protocol MUST NOT be used without any security mechanism (TLS or IPsec). described in the specification. SCTP Guidelines
The following are guidelines for Diameter implementations that support SCTP: 1.
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. See Sections 13. Diameter servers MUST support TLS and IPsec. An implementation MAY add arbitrary non-mandatory AVPs to any command defined in an application.

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2. which is used in the message forwarding process. Diameter relay and proxy agents are responsible for finding an upstream server that supports the application of a particular message.3). If none can be found. which are terms used extensively throughout this document. A session is a logical concept at the application layer. Connections vs. et al. Diameter nodes inform their peers of locally supported applications. A connection is a transport level connection between two peers. while all other Diameter nodes MUST advertise locally supported applications.5. all Diameter messages contain an Application Identifier. The receiver of a Capabilities Exchange message advertising Relay service MUST assume that the sender supports all current and future applications. and is identified via the Session-Id AVP
Calhoun.
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. used to send and receive Diameter messages. 2.
Application Identifiers
Each Diameter application MUST have an IANA assigned Application Identifier (see Section 11. The following Application Identifier values are defined: Diameter Common Messages NASREQ Mobile-IP Diameter Base Accounting Relay 0 1 [NASREQ] 2 [DIAMMIP] 3 0xffffffff
Relay and redirect agents MUST advertise the Relay Application Identifier. During the capabilities exchange. Furthermore.4. and is shared between an access device and a server. The base protocol does not require an Application Identifier since its support is mandatory. an error message is returned with the Result-Code AVP set to DIAMETER_UNABLE_TO_DELIVER. Sessions
This section attempts to provide the reader with an understanding of the difference between connection and session.

RFC 3588

Diameter Based Protocol

September 2003

+--------+ +-------+ +--------+ | Client | | Relay | | Server | +--------+ +-------+ +--------+ <----------> <----------> peer connection A peer connection B <-----------------------------> User session x Figure 1: Diameter connections and sessions In the example provided in Figure 1, peer connection A is established between the Client and its local Relay. Peer connection B is established between the Relay and the Server. User session X spans from the Client via the Relay to the Server. Each "user" of a service causes an auth request to be sent, with a unique session identifier. Once accepted by the server, both the client and the server are aware of the session. It is important to note that there is no relationship between a connection and a session, and that Diameter messages for multiple sessions are all multiplexed through a single connection. 2.6. Peer Table

The Diameter Peer Table is used in message forwarding, and referenced by the Realm Routing Table. A Peer Table entry contains the following fields: Host identity Following the conventions described for the DiameterIdentity derived AVP data format in Section 4.4. This field contains the contents of the Origin-Host (Section 6.3) AVP found in the CER or CEA message. StatusT This is the state of the peer entry, and MUST match one of the values listed in Section 5.6. Static or Dynamic Specifies whether a peer entry was statically configured, or dynamically discovered. Expiration time Specifies the time at which dynamically discovered peer table entries are to be either refreshed, or expired.

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RFC 3588

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September 2003

TLS Enabled Specifies whether TLS is to be used when communicating with the peer. Additional security information, when needed (e.g., keys, certificates) 2.7. Realm-Based Routing Table

All Realm-Based routing lookups are performed against what is commonly known as the Realm Routing Table (see Section 12). A Realm Routing Table Entry contains the following fields: Realm Name This is the field that is typically used as a primary key in the routing table lookups. Note that some implementations perform their lookups based on longest-match-from-the-right on the realm rather than requiring an exact match. Application Identifier An application is identified by a vendor id and an application id. For all IETF standards track Diameter applications, the vendor id is zero. A route entry can have a different destination based on the application identification AVP of the message. This field MUST be used as a secondary key field in routing table lookups. Local Action The Local Action field is used to identify how a message should be treated. The following actions are supported: 1. LOCAL - Diameter messages that resolve to a route entry with the Local Action set to Local can be satisfied locally, and do not need to be routed to another server. 2. RELAY - All Diameter messages that fall within this category MUST be routed to a next hop server, without modifying any non-routing AVPs. See Section 6.1.8 for relaying guidelines 3. PROXY - All Diameter messages that fall within this category MUST be routed to a next hop server. The local server MAY apply its local policies to the message by including new AVPs to the message prior to routing. See Section 6.1.8 for proxying guidelines. 4. REDIRECT - Diameter messages that fall within this category MUST have the identity of the home Diameter server(s) appended, and returned to the sender of the message. See Section 6.1.7 for redirect guidelines.

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RFC 3588

Diameter Based Protocol

September 2003

Server Identifier One or more servers the message is to be routed to. These servers MUST also be present in the Peer table. When the Local Action is set to RELAY or PROXY, this field contains the identity of the server(s) the message must be routed to. When the Local Action field is set to REDIRECT, this field contains the identity of one or more servers the message should be redirected to. Static or Dynamic Specifies whether a route entry was statically configured, or dynamically discovered. Expiration time Specifies the time which a dynamically discovered route table entry expires. It is important to note that Diameter agents MUST support at least one of the LOCAL, RELAY, PROXY or REDIRECT modes of operation. Agents do not need to support all modes of operation in order to conform with the protocol specification, but MUST follow the protocol compliance guidelines in Section 2. Relay agents MUST NOT reorder AVPs, and proxies MUST NOT reorder AVPs. The routing table MAY include a default entry that MUST be used for any requests not matching any of the other entries. The routing table MAY consist of only such an entry. When a request is routed, the target server MUST have advertised the Application Identifier (see Section 2.4) for the given message, or have advertised itself as a relay or proxy agent. Otherwise, an error is returned with the Result-Code AVP set to DIAMETER_UNABLE_TO_DELIVER. 2.8. Role of Diameter Agents

In addition to client and servers, the Diameter protocol introduces relay, proxy, redirect, and translation agents, each of which is defined in Section 1.3. These Diameter agents are useful for several reasons: They can distribute administration of systems to a configurable grouping, including the maintenance of security associations. They can be used for concentration of requests from an number of co-located or distributed NAS equipment sets to a set of like user groups. They can do value-added processing to the requests or responses.

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and its state is considered active either until it is notified otherwise.RFC 3588
Diameter Based Protocol
September 2003
-
They can be used for load balancing. RADIUS <-> Diameter) Limiting resources authorized to a particular user Per user or transaction auditing
A Diameter agent MAY act in a stateful manner for some requests and be stateless for others. they can sort requests and forward towards the correct target.g.
The Diameter protocol requires that agents maintain transaction state. Transaction state implies that upon forwarding a request.7. Each authorized session has an expiration. A Diameter implementation MAY act as one type of agent for some requests. the field is replaced with a locally unique identifier. A stateless agent is one that only maintains transaction state. 2. The Proxy-Info AVP allows stateless agents to add local state to a Diameter request. A complex network will have multiple authentication sources. A stateful agent is one that maintains session state information.
Calhoun. This routing decision is performed using a list of supported realms. such as: Protocol translation (e.8.
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. or by expiration.. This is known as the Realm Routing Table.. by keeping track of all authorized active sessions. which is communicated by Diameter servers via the Session-Timeout AVP. which is restored to its original value when the corresponding answer is received. The request’s state is released upon receipt of the answer. Each authorized session is bound to a particular service.g. et al. and as another type of agent for others. the protocol’s failover procedures require that agents maintain a copy of pending requests. Relay Agents
Relay Agents are Diameter agents that accept requests and route messages to other Diameter nodes based on information found in the messages (e. as is defined further in Section 2. Maintaining session state MAY be useful in certain applications. However. Destination-Realm). which is used for failover purposes. and known peers. its Hop-by-Hop identifier is saved. with the guarantee that the same state will be present in the answer.1.

this reduces the configuration load on Diameter servers that would otherwise be necessary when NASes are added. Since Relays do not perform any application level processing. Prior to issuing the request. Answer <--------+------+ | | | DRL | | | +------+ example. they provide relaying services for all Diameter applications. Relays modify Diameter messages by inserting and removing routing information. access devices) to enforce resource usage.com’s Home Diameter Server. 2. Request 4. but do not modify any other portion of a message. Proxy Agents
Similarly to relays. Request 3.net ---------> 1.
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. which is an access device. Answer <--------+------+ | | | HMS | | | +------+ example. HMS identifies that the request can be locally supported (via the realm).. for the user bob@example. This requires that proxies maintain the state of their downstream peers (e. and provisioning. et al. they differ since they modify messages to implement policy enforcement.com
Figure 2: Relaying of Diameter messages The example provided in Figure 2 depicts a request issued from NAS. and replies with an answer. +------+ | | | NAS | | | +------+ example.com" as the key.RFC 3588
Diameter Based Protocol
September 2003
Relays MAY be used to aggregate requests from multiple Network Access Servers (NASes) within a common geographical area (POP).2. and relays the message to HMS. DRL performs the same route lookup as NAS. processes the authentication and/or authorization request. which is example. NAS performs a Diameter route lookup.
Calhoun. Relays SHOULD NOT maintain session state but MUST maintain transaction state. proxy agents route Diameter messages using the Diameter Routing Table. which is routed back to NAS using saved transaction state. Likewise. changed or deleted. and determines that the message is to be relayed to DRL. and therefore MUST advertise the Relay Application Identifier. However. The use of Relays is advantageous since it eliminates the need for NASes to be configured with the necessary security information they would otherwise require to communicate with Diameter servers in other realms.8. provide admission control. using "example.net ---------> 2. which is a Diameter Relay.g.com.

DRL has a default route configured to DRD. 2. Proxies MUST only advertise the Diameter applications they support.com. and make allocation and admission decisions according to their configuration. The example provided in Figure 3 depicts a request issued from the access device. Since redirect agents do not relay messages.8. which is a redirect agent that returns a redirect notification to DRL. An example is a redirect agent that provides services to all members of a consortium. Since redirect agents do not receive answer messages. since redirect agents never relay requests. if one doesn’t already exist. and forwards the request to it. which does not have a routing entry in its Diameter Routing Table for example. but does not wish to be burdened with relaying all messages between realms. Proxies MAY be used in call control centers or access ISPs that provide outsourced connections. Since enforcing policies requires an understanding of the service being provided. since modifying messages breaks authentication. they cannot maintain session state. they are not required to maintain transaction state.RFC 3588
Diameter Based Protocol
September 2003
It is important to note that although proxies MAY provide a value-add function for NASes. Further.
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. and only return an answer with the information necessary for Diameter agents to communicate directly.com. they do not allow access devices to use end-toend security. Proxies that wish to limit resources MUST maintain session state. et al. Upon receipt of the redirect notification. This scenario is advantageous since it does not require that the consortium provide routing updates to its members when changes are made to a member’s infrastructure. Redirect Agents
Redirect agents are useful in scenarios where the Diameter routing configuration needs to be centralized. All proxies MUST maintain transaction state. they do not modify messages. The message is forwarded by the NAS to its relay. DRL.
Calhoun. they can monitor the number and types of ports in use. NAS. DRL establishes a transport connection with HMS. as well as HMS’ contact information.3. for the user bob@example.

Use end-to-end security on messages containing sensitive AVPs. Which AVPs are sensitive is determined by service provider policy. Always use end-to-end security. may be applied by next hop Diameter peer or by destination realm.
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It is strongly RECOMMENDED that all Diameter implementations support end-to-end security.10. each connection is authenticated. et al. The circumstances requiring the use of end-to-end security are determined by policy on each of the peers.
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. Accounting AVPs may be considered sensitive.2. AVPs containing keys and passwords should be considered sensitive. Diameter requires transmission level security to be used on each connection (TLS or IPsec). Diameter Path Authorization
As noted in Section 2. End-to-end security is provided via the End-to-End security extension. there may be no need for end-to-end security. Before initiating a connection. described in [AAACMS]. replay and integrity protected and confidential on a per-packet basis. For example.
End-to-End Security Framework
End-to-end security services include confidentiality and message origin authentication. These services are provided by supporting AVP integrity and confidentiality between two peers.9. For example.RFC 3588
Diameter Based Protocol
September 2003
2. Security policies. a Diameter Peer MUST check that its peers are authorized to act in their roles. In addition to authenticating each connection. 2. Therefore. End-to-end security policies include: Never use end-to-end security. a Diameter peer may be authentic.
Calhoun. but that does not mean that it is authorized to act as a Diameter Server advertising a set of Diameter applications. which are not the subject of standardization. each connection as well as the entire session MUST also be authorized. where TLS or IPsec transmissionlevel security is sufficient. communicating through agents. Any AVP for which the P bit may be set or which may be encrypted may be considered sensitive.

a Diameter client receiving an authorization response for a service that it cannot perform MUST NOT substitute an alternate service. If the service cannot be provided by the local realm. the home Diameter server is implicitly indicating its willingness to engage in the business transaction as specified by the contractual relationship between the server and the previous hop. By authorizing a request. Accounting requests without corresponding authorization responses SHOULD be subjected to further scrutiny. then a DIAMETER_UNABLE_TO_COMPLY error message MUST be sent within the accounting request. by establishing credit limits for intermediate realms and refusing to accept responses which would violate those limits. prior to authorizing a session. Diameter capabilities negotiation (CER/CEA) also MUST be carried out.RFC 3588
Diameter Based Protocol
September 2003
Prior to bringing up a connection.8.
Calhoun. By issuing an accounting request corresponding to the authorization response. the local Diameter agent. as should accounting requests indicating a difference between the requested and provided service. For example. The home Diameter server. MUST check the Route-Record AVPs to make sure that the route traversed by the response is acceptable. et al. As noted in Section 6.5) is sent if the route traversed by the request is unacceptable. in order to determine what Diameter applications are supported by each peer.1. The AVP contains the identity of the peer the request was received from.
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. Diameter sessions MUST be routed only through authorized nodes that have advertised support for the Diameter application required by the session. the local realm implicitly indicates its agreement to provide the service indicated in the authorization response. A local realm may wish to limit this exposure. on receiving a Diameter response authorizing a session. At each step.1. authorization checks are performed at each connection along the path. and then send accounting requests for the alternate service instead. A home realm may also wish to check that each accounting request message corresponds to a Diameter response authorizing the session. forwarding of an authorization response is considered evidence of a willingness to take on financial risk relative to the session. A DIAMETER_AUTHORIZATION_REJECTED error message (see Section 7. Similarly. for example. MUST check the Route-Record AVPs to make sure that the route traversed by the request is acceptable. a relay or proxy agent MUST append a Route-Record AVP to all requests forwarded. administrators within the home realm may not wish to honor requests that have been routed through an untrusted realm.

This flag MUST NOT be set if an error answer message (e. Diameter agents that receive a request with the T flag set. T(Potentially re-transmitted message) .777. The 24-bit address space is managed by IANA (see Section 11.3 for the possible values that the application-id may use. Diameter agents only need to be concerned about the number of requests they send based on a single received request. an accounting application or a vendor specific application. and is used in order to communicate the command associated with the message. Command-Code values 16.
Calhoun.these flag bits are reserved for future use. See Section 7. The application can be an authentication application.2. and ignored by the receiver.777.2. Application-ID Application-ID is four octets and is used to identify to which application the message is applicable for.1). otherwise the sender MUST set this flag. to aid the removal of duplicate requests. MUST keep the T flag set in the forwarded request. retransmissions by other entities need not be tracked..This flag is set after a link failover procedure.215 (hexadecimal values FFFFFE -FFFFFF) are reserved for experimental use (See Section 11. This bit MUST NOT be set in request messages. This flag MUST NOT be set in answer messages.3).214 and 16. et al.RFC 3588
Diameter Based Protocol
September 2003
bit set are commonly referred to as error messages. and MUST be set to zero. See Section 11. This bit MUST be cleared when sending a request for the first time. The application-id in the header MUST be the same as what is contained in any relevant AVPs contained in the message. as an indication of a possible duplicate due to a link failure. r(eserved) . It can be set only in cases where no answer has been received from the server for a request and the request is sent again.
Command-Code The Command-Code field is three octets. It is set when resending requests not yet acknowledged.g.
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. a protocol error) has been received for the earlier message.

even across reboots. The End-to-End Identifier MUST NOT be modified by Diameter agents of any kind. Duplicate answer messages that are to be locally consumed (see Section 6. The Hop-by-Hop identifier is normally a monotonically increasing number. The identifier MUST remain locally unique for a period of at least 4 minutes. whose start value was randomly generated. et al. The combination of the Origin-Host (see Section 6. Upon reboot implementations MAY set the high order 12 bits to contain the low order 12 bits of current time.RFC 3588
Diameter Based Protocol
September 2003
Hop-by-Hop Identifier The Hop-by-Hop Identifier is an unsigned 32-bit integer field (in network byte order) and aids in matching requests and replies. and the low order 20 bits to a random value. Senders of request messages MUST insert a unique identifier on each message. The sender MUST ensure that the Hop-by-Hop identifier in a request is unique on a given connection at any given time. End-to-End Identifier The End-to-End Identifier is an unsigned 32-bit integer field (in network byte order) and is used to detect duplicate messages. An answer message that is received with an unknown Hop-by-Hop Identifier MUST be discarded. AVPs AVPs are a method of encapsulating information relevant to the Diameter message. Duplicate requests SHOULD cause the same answer to be transmitted (modulo the hop-by-hop Identifier field and any routing AVPs that may be present).2) SHOULD be silently discarded. The sender of an Answer message MUST ensure that the Hop-by-Hop Identifier field contains the same value that was found in the corresponding request. and MUST NOT affect any state that was set when the original request was processed. See Section 4 for more information on AVPs. and MAY attempt to ensure that the number is unique across reboots.
Calhoun. The originator of an Answer message MUST ensure that the End-to-End Identifier field contains the same value that was found in the corresponding request.3) and this field is used to detect duplicates.
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.

then 0 or 1 such AVP may be . The AVP can . ICV at the end). The default value is zero. required. = 1*DIGIT . RFC 2234 Section 6. be present. The string "AVP" stands for *any* arbitrary .
qual
min
max
A
avp-spec
avp-name
Calhoun. then exactly one such AVP MUST . in the base or extended Diameter . The default value is infinity. in a fixed or required rule. . it precedes a fixed. The avp-spec has to be an AVP Name. These braces cannot be used to express . . = avp-spec / "AVP" . required or fixed position AVPs defined in . optional fixed rules (such as an optional . qualifier. rule. NOTE: "[" and "]" have a different meaning .RFC 3588
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September 2003
optional
= [qual] "[" avp-name "]" .
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. is ’0*1fixed’. . be present. See ABNF conventions. The maximum number of times the element may . be present. The avp-name in the ’optional’ rule cannot . = [min] "*" [max] . To do this. present. the convention . If an optional rule has no . qualifier. = diameter-name . evaluate to any AVP Name which is included . which does not conflict with the . above). AVP Name. = 1*DIGIT . . The minimum number of times the element may . et al. appear anywhere in the message. present. . or optional . the command code definition. defined . If a fixed or required rule has no . value of zero implies the AVP MUST NOT be .6. The absence of any qualifiers depends on whether . specifications. than in ABNF (see the optional rule.

Both the request and the answer for a given command share the same command code. The receiver could not process the request. while the acronyms are STR and STA. to ask that a particular action be performed. The request is identified by the R(equest) bit in the Diameter header set to one (1). routing and security information as well as configuration details for the request and reply. known as redirect. Some AVPs MAY be listed more than once. MAY also be included in answer messages. accounting. Each English word is delimited by a hyphen. PXY > User-Name } Origin-Host } AVP
Diameter Command Naming Conventions
Diameter command names typically includes one or more English words followed by the verb Request or Answer. Diameter AVPs Diameter AVPs carry specific authentication.RFC 3588
Diameter Based Protocol
September 2003
The following is a definition of a fictitious command code: Example-Request ::= < { * { * [ 3. encoded within AVPs. Once the receiver has completed the request it issues the corresponding answer. A three-letter acronym for both the request and answer is also normally provided. such as authorizing a user or terminating a session. "Diameter-Header: 9999999. et al. 4. but provides information about a Diameter peer that is able to satisfy the request.3. The command name is Session-Terminate-Request and Session-Terminate-Answer. The effect of such an AVP is specific. respectively. which includes a result code that communicates one of the following: The request was successful The request failed An additional request must be sent to provide information the peer requires prior to returning a successful or failed answer.
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Additional information. REQ. authorization. and is specified in each case by the AVP description. An example is a message set used to terminate a session.
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.
Calhoun.

A number of zerovalued bytes are added to the end of the AVP Data field till a word boundary is reached.. The length of the padding is not reflected in the AVP Length field. and an unrecognized bit SHOULD be considered an error. Diameter Relay and redirect agents MUST NOT reject messages with unrecognized AVPs.
Calhoun. The ’r’ (reserved) bits are unused and SHOULD be set to 0. which are allocated by IANA (see Section 11. format of the header is: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AVP Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |V M P r r r r r| AVP Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor-ID (opt) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data . without setting the Vendor-Id field. AVP Header The
The fields in the AVP header MUST be sent in network byte order. combined with the Vendor-Id field. +-+-+-+-+-+-+-+-+
AVP Code The AVP Code. known as the Mandatory bit.RFC 3588
Diameter Based Protocol
September 2003
Each AVP of type OctetString MUST be padded to align on a 32-bit boundary.1. et al. or translation agent and either the AVP or its value is unrecognized. AVP numbers 256 and above are used for Diameter. AVP Flags The AVP Flags field informs the receiver how each attribute must be handled. identifies the attribute uniquely. server. the message MUST be rejected. The ’P’ bit indicates the need for encryption for end-to-end security. proxy. while other AVP types align naturally.
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. AVP numbers 1 through 255 are reserved for backward compatibility with RADIUS.1). 4. Note that subsequent Diameter applications MAY define additional bits within the AVP Header. If an AVP with the ’M’ bit set is received by a Diameter client.. indicates whether support of the AVP is required. The ’M’ Bit.

known as the Vendor-Specific bit. or whose value is not supported. et al. In order to preserve interoperability. Unless otherwise noted. a Diameter implementation MUST be able to exclude from a Diameter message any Mandatory AVP which is neither defined in the base Diameter protocol nor in any of the Diameter Application specifications governing the message in which it appears.RFC 3588
Diameter Based Protocol
September 2003
The ’M’ bit MUST be set according to the rules defined for the AVP containing it. and indicates the number of octets in this AVP including the AVP Code. the implementation may resend the message without the AVP. per peer. AVP Flags. Thus an administrator could change the configuration to avoid interoperability problems. The ’V’ bit.
Calhoun.
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. AVP Length. 2) A configuration option may be provided on a system wide. AVPs will have the following default AVP Flags field settings: The ’M’ bit MUST be set. the message SHOULD be rejected. possibly inserting additional standard AVPs instead. If a message is received with an invalid attribute length. indicates whether the optional Vendor-ID field is present in the AVP header. Diameter implementations are required to support all Mandatory AVPs which are allowed by the message’s formal syntax and defined either in the base Diameter standard or in one of the Diameter Application specifications governing the message. or per realm basis that would allow/prevent particular Mandatory AVPs to be sent. Vendor-ID field (if present) and the AVP data. When set the AVP Code belongs to the specific vendor code address space.
AVP Length The AVP Length field is three octets. It MAY do this in one of the following ways: 1) If a message is rejected because it contains a Mandatory AVP which is neither defined in the base Diameter standard nor in any of the Diameter Application specifications governing the message in which it appears. The ’V’ bit MUST NOT be set. AVPs with the ’M’ bit cleared are informational only and a receiver that receives a message with such an AVP that is not supported. MAY simply ignore the AVP.

This field is only present if the respective bit-flag is enabled.
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. in network byte order. Basic AVP Data Formats
The Data field is zero or more octets and contains information specific to the Attribute. The AVP Length field MUST be set to 16 (20 if the ’V’ bit is enabled). AVP Values of this type that are not a multiple of four-octets in length is followed by the necessary padding so that the next AVP (if any) will start on a 32-bit boundary. implementations MUST NOT use the zero (0) vendor ID. a new version of this RFC must be created.1. encoded in network byte order. Integer64 64 bit signed value.1. Integer32 32 bit signed value.
Optional Header Elements
The AVP Header contains one optional field. in network byte order. Any vendor wishing to implement a vendor-specific Diameter AVP MUST use their own Vendor-ID along with their privately managed AVP address space. guaranteeing that they will not collide with any other vendor’s vendor-specific AVP(s). The optional four-octet Vendor-ID field contains the IANA assigned "SMI Network Management Private Enterprise Codes" [ASSIGNNO] value.RFC 3588
Diameter Based Protocol
September 2003
4.
Calhoun. Since the absence of the vendor ID field implies that the AVP in question is not vendor specific. nor with future IETF applications.2. as managed by the IANA. Vendor-ID The Vendor-ID field is present if the ’V’ bit is set in the AVP Flags field. The AVP Length field MUST be set to 12 (16 if the ’V’ bit is enabled). et al. The format of the Data field MUST be one of the following base data types or a data type derived from the base data types. In the event that a new Basic AVP Data Format is needed. the AVP Length field MUST be set to at least 8 (12 if the ’V’ bit is enabled). OctetString The data contains arbitrary data of variable length. A vendor ID value of zero (0) corresponds to the IETF adopted AVP values. Unless otherwise noted. 4. The format and length of the Data field is determined by the AVP Code and AVP Length fields.

3. 4. Grouped The Data field is specified as a sequence of AVPs. It is a discriminated union.
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. The first two octets of the Address
Calhoun.RFC 3588
Diameter Based Protocol
September 2003
Unsigned32 32 bit unsigned value. Derived AVP Data Formats
In addition to using the Basic AVP Data Formats. including their headers and padding. The AVP Length field MUST be set to 12 (16 if the ’V’ bit is enabled). An application that defines new AVP Derived Data Formats MUST include them in a section entitled "AVP Derived Data Formats". Address The Address format is derived from the OctetString AVP Base Format. in network byte order. using the same format as the definitions below.in the order in which they are specified including their headers and padding. The AVP Length field is set to 8 (12 if the ’V’ bit is enabled) plus the total length of all included AVPs. most significant octet first. applications may define data formats derived from the Basic AVP Data Formats. The below AVP Derived Data Formats are commonly used by applications. representing. Float32 This represents floating point values of single precision as described by [FLOATPOINT]. Unsigned64 64 bit unsigned value. for example a 32-bit (IPv4) [IPV4] or 128-bit (IPv6) [IPV6] address. Each new definition must be either defined or listed with a reference to the RFC that defines the format. The 64-bit value is transmitted in network byte order. Thus the AVP length field of an AVP of type Grouped is always a multiple of 4. et al. The AVP Length field MUST be set to 16 (20 if the ’V’ bit is enabled). in network byte order. The 32-bit value is transmitted in network byte order. The AVP Length field MUST be set to 12 (16 if the ’V’ bit is enabled). Float64 This represents floating point values of double precision as described by [FLOATPOINT]. The AVP Length field MUST be set to 16 (20 if the ’V’ bit is enabled). Each of these AVPs follows .

Since additional code points are added by amendments to the 10646 standard from time to time. UTF-8 may require multiple bytes to represent a single character / code point. in the same format as the first four bytes are in the NTP timestamp format. The use of leading or trailing white space SHOULD be avoided. This is a human readable string represented using the ISO/IEC IS 10646-1 character set. 7 February 2036 the time value will overflow. encoded as an OctetString using the UTF-8 [UFT8] transformation format described in RFC 2279. implementations MUST be prepared to encounter any code point from 0x00000001 to 0x7fffffff. On 6h 28m 16s UTC. The string MUST contain four octets. Time The Time format is derived from the OctetString AVP Base Format. not characters. thus the length of an UTF8String in octets may be different from the number of characters encoded.
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. the UTF-8 charset is identical to the US-ASCII charset. For information encoded in 7-bit US-ASCII. The AddressType is used to discriminate the content and format of the remaining octets. an alternative means of entry and display. UTF8String The UTF8String format is derived from the OctetString AVP Base Format. This procedure MUST be supported by all DIAMETER nodes. et al. MAY be provided. SNTP [SNTP] describes a procedure to extend the time to 2104. which contains an Address Family defined in [IANAADFAM]. the control code sequence CR LF SHOULD be used. For code points not directly supported by user interface hardware or software. When it is necessary to represent a new line. such as hexadecimal.RFC 3588
Diameter Based Protocol
September 2003
AVP represents the AddressType.
Calhoun. Note that the AVP Length field of an UTF8String is measured in octets. The NTP Timestamp format is defined in chapter 3 of [SNTP]. The use of control codes SHOULD be avoided. This represents the number of seconds since 0h on 1 January 1900 with respect to the Coordinated Universal Time (UTC). Byte sequences that do not correspond to the valid encoding of a code point into UTF-8 charset or are outside this range are prohibited.

= ". whatever the connection it is sent on.
Calhoun. If absent. transport .
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. No transport security "aaas://" FQDN [ port ] [ transport ] [ protocol ] . . . a single FQDN should be picked at startup. If multiple Diameter nodes run on the same host. DiameterURI The DiameterURI MUST follow the Uniform Resource Identifiers (URI) syntax [URI] rules specified below: "aaa://" FQDN [ port ] [ transport ] [ protocol ] . Transport security used FQDN port . et al.transport=" transport-protocol One of the transports used to listen for incoming connections. each Diameter node MUST be assigned a unique DiameterIdentity. . If absent. the default SCTP [SCTP] protocol is assumed. = Fully Qualified Host Name = ":" 1*DIGIT One of the ports used to listen for incoming connections. . . UDP MUST NOT be used when the aaa-protocol field is set to diameter.RFC 3588
Diameter Based Protocol
September 2003
DiameterIdentity The DiameterIdentity format is derived from the OctetString AVP Base Format. If a Diameter node can be identified by several FQDNs. . the default Diameter port (3868) is assumed. . . DiameterIdentity = FQDN
DiameterIdentity value is used to uniquely identify a Diameter node for purposes of duplicate connection and routing loop detection. . The contents of the string MUST be the FQDN of the Diameter node. and used as the only DiameterIdentity for that node.

com:6666.
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[Page 45]
. The definition contains a list of valid values and their interpretation and is described in the Diameter application introducing the AVP.transport=udp.protocol=" aaa-protocol .transport=tcp. the packet is dropped if the evaluated was a permit.example. If absent. Each packet is once.com.protocol=diameter aaa://host. et al.transport=tcp aaa://host.com:6666.protocol=diameter aaa://host. and passed if the last rule was
Calhoun.example.com:6666.com:1813.protocol=radius Enumerated Enumerated is derived from the Integer32 AVP Base Format.com. Packets may be filtered based on the following information that is associated with it: Direction Source and destination IP address Protocol Source and destination port TCP flags IP fragment flag IP options ICMP types Rules for the first evaluated last rule a deny. with matched rule terminating the evaluation.example. (in or out) (possibly masked) (lists or ranges)
the appropriate direction are evaluated in order. the default AAA protocol .RFC 3588
Diameter Based Protocol
September 2003
transport-protocol = ( "tcp" / "sctp" / "udp" ) protocol = ".transport=tcp aaa://host.example.example.example. aaa-protocol = ( "diameter" / "radius" / "tacacs+" )
The following are examples of valid Diameter host identities: aaa://host. is diameter. IPFilterRule The IPFilterRule format is derived from the OctetString AVP Base Format. If no rule matches.protocol=diameter aaa://host. It uses the ASCII charset.

For a match to occur. To test for a particular IP version.255 will match. ipno/bits An IP number as above with a mask width of the form 1. This does not affect the selection of port numbers.0 to 1. The "ip" keyword means any protocol will match.0.2. "in" is from the terminal. causing all other addresses to be matched instead.0/0 or the IPv6 equivalent. all IP numbers from 1.Drop packets that match the rule. "out" is to the terminal. In this case.4/24. The keyword "assigned" is the address or set of addresses assigned to the terminal. Only this exact IP number will match the rule. For IPv4. An IP protocol specified by number.3. <address/mask> [ports] The <address/mask> may be specified as: ipno An IPv4 or IPv6 number in dottedquad or canonical IPv6 form. et al. the bits part can be set to zero.0.Allow packets that match the rule. the same IP version must be present in the packet that was used in describing the IP address. The keyword "any" is 0.3. a typical first rule is often "deny in ip! assigned" The sense of the match can be inverted by preceding an address with the not modifier (!).
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[Page 46]
. The bit width MUST be valid for the IP version and the IP number MUST NOT have bits set beyond the mask.2. deny .RFC 3588
Diameter Based Protocol
September 2003
IPFilterRule filters MUST follow the format: action dir proto from src to dst [options] action permit .
dir
proto
src and dst
Calhoun.2.3.

ipoptions spec Match if the IP header contains the comma separated list of options specified in spec.e. ts (rfc1323 timestamp) and cc (rfc1644 t/tcp connection count).
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[Page 47]
. lsrr (loose source route). Match packets that have the SYN bit set but no ACK bit. frag may not be used in conjunction with either tcpflags or TCP/UDP port specifications. sack (selective ack).]] The ’-’ notation specifies a range of ports (including boundaries). options: frag
Match if the packet is a fragment and this is not the first fragment of the datagram... UDP and SCTP protocols. not the first fragment) will never match a rule that has one or more port specifications. rr (record packet route) and ts (timestamp). See the frag option for details on matching fragmented packets. The absence of a particular option may be denoted with a ’!’. or ACK bits set.RFC 3588
Diameter Based Protocol
September 2003
With the TCP. optional ports may be specified as: {port/port-port}[.. supported TCP options are:
The
mss (maximum segment size).
Calhoun. setup
Match packets that have the RST
TCP packets only. window (tcp window advertisement). established TCP packets only. supported IP options are:
The
ssrr (strict source route). et al. tcpoptions spec Match if the TCP header contains the comma separated list of options specified in spec. The absence of a particular option may be denoted with a ’!’.ports[. Fragmented packets that have a non-zero offset (i..

router advertisement (9).
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[Page 48]
.c code may provide a useful base for implementations. timestamp request (13).RFC 3588
Diameter Based Protocol
September 2003
tcpflags spec TCP packets only. An access device that is unable to interpret or apply a deny rule MUST terminate the session. There is one kind of packet that the access device MUST always discard. and the ipfw. A rule that contains a tcpflags specification can never match a fragmented packet that has a non-zero offset. router solicitation (10). information request (15). Match if the ICMP type is in the list types. source quench (4). ack and urg. that is an IP fragment with a fragment offset of one. This is a valid packet. IP header bad (12). echo request (8). redirect (5). psh. address mask request (17) and address mask reply (18). time-to-live exceeded (11). The supported TCP flags are: fin. The list may be specified as any combination of ranges or individual types separated by commas. Both the numeric values and the symbolic values listed below can be used. syn. timestamp reply (14). destination unreachable (3). icmptypes types ICMP packets only. The supported ICMP types are: echo reply (0).
Calhoun. et al. but it only has one use. The absence of a particular flag may be denoted with a ’!’. Match if the TCP header contains the comma separated list of flags specified in spec. The rule syntax is a modified subset of ipfw(8) from FreeBSD. rst. for example to protect the access device owner’s infrastructure. to try to circumvent firewalls. See the frag option for details on matching fragmented packets. An access device that is unable to interpret or apply a permit rule MAY apply a more restrictive rule. An access device MAY apply deny rules of its own before the supplied rules. information reply (16).

meter
dir
The format is as described under IPFilterRule.RFC 3588
Diameter Based Protocol
September 2003
QoSFilterRule The QosFilterRule format is derived from the OctetString AVP Base Format. src and dst The format is as described under IPFilterRule. to nest them. with the first matched rule terminating the evaluation.
Grouped AVP Values
The Diameter protocol allows AVP values of type ’Grouped. proto The format is as described under IPFilterRule. the packet is treated as best effort. AVPs within an AVP of type Grouped have the same padding requirements as non-Grouped AVPs. that is.4. It uses the ASCII charset. .Mark packet with a specific DSCP [DIFFSERV]. Each packet is evaluated once.’ This implies that the Data field is actually a sequence of AVPs. QoSFilterRule filters MUST follow the format: action dir proto from src to dst [options] tag . An access device that is unable to interpret or apply a QoS rule SHOULD NOT terminate the session. The metering options MUST be included. Packets may be marked or metered based on the following information that is associated with it: Direction Source and destination IP address Protocol Source and destination port DSCP values (in or out) (possibly masked) (lists or ranges) (no mask or range)
Rules for the appropriate direction are evaluated in order. It is possible to include an AVP with a Grouped type within a Grouped type. The DSCP option MUST be included. as defined in Section 4.Meter traffic.
4.
Calhoun. If no rule matches.
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. et al.

In this case:
Calhoun. The Origin-Host AVP is required (Section 6. If absent. using ABNF [ABNF] (with modifications). specifications. Further. grouped-avp-def name-fmt name = name "::=" avp = ALPHA *(ALPHA / DIGIT / "-") = name-fmt . The Vendor-ID assigned to the Grouped AVP.com". the Grouped AVP itself MUST also include the ’M’ bit set. as defined below. The AVP Code assigned to the Grouped AVP = 1*DIGIT . . . the default value of zero is .3).
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[Page 50]
. The Grouped Data field has the following ABNF grammar: Example-AVP ::= < { 1*{ *[ AVP Header: 999999 > Origin-Host } Session-Id } AVP ]
An Example-AVP with Grouped Data follows.RFC 3588
Diameter Based Protocol
September 2003
The AVP Code numbering space of all AVPs included in a Grouped AVP is the same as for non-grouped AVPs.
Example AVP with a Grouped Data type
The Example-AVP (AVP Code 999999) is of type Grouped and is used to clarify how Grouped AVP values work. defined in the base or extended Diameter . et al. = header [ *fixed] [ *required] [ *optional] [ *fixed] = "<" "AVP-Header:" avpcode [vendor] ">" = 1*DIGIT . Every Grouped AVP defined MUST include a corresponding grammar.4. Origin-Host = "example. if any of the AVPs encapsulated within a Grouped AVP has the ’M’ (mandatory) bit set.1. used. The name has to be the name of an AVP.
avp
header avpcode
vendor
4.

example.2358.com:33054.
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[Page 51]
.com:33041.0AF3B82" optional AVPs included are Recovery-Policy = <binary> 2163bc1d0ad82371f6bc09484133c3f09ad74a0dd5346d54195a7cf0b35 2cabc881839a4fdcfbc1769e2677a4c1fb499284c5f70b48f58503a45c5 c2d6943f82d5930f2b7c1da640f476f0e9c9572a50db8ea6e51e1c2c7bd f8bb43dc995144b8dbe297ac739493946803e1cee3e15d9b765008a1b2a cf4ac777c80041d72c01e691cf751dbf86e85f509f3988e5875dc905119 26841f00f0e29a6d1ddc1a842289d440268681e052b30fb638045f7779c 1d873c784f054f688f5001559ecff64865ef975f3e60d2fd7966b8c7f92 Futuristic-Acct-Record = <binary> fe19da5802acd98b07a5b86cb4d5d03f0314ab9ef1ad0b67111ff3b90a0 57fe29620bf3585fd2dd9fcc38ce62f6cc208c6163c008f4258d1bc88b8 17694a74ccad3ec69269461b14b2e7a4c111fb239e33714da207983f58c 41d018d56fe938f3cbf089aac12a912a2f0d1923a9390e5f789cb2e5067 d3427475e49968f841 The data for the optional AVPs is represented in hex since the format of these AVPs is neither known at the time of definition of the Example-AVP group.except by Diameter implementations which support the same set of AVPs.23561. et al. the Recover-Policy and Futuristic-Acct-Record AVPs). The encoding example illustrates how padding is used and how length fields are calculated.
Calhoun. nor (likely) at the time when the example instance of this AVP is interpreted .RFC 3588
Diameter Based Protocol
September 2003
One or more Session-Ids must follow. Also note that AVPs may be present in the Grouped AVP value which the receiver cannot interpret (here.
Here there are two:
Session-Id = "grump.893.23432.0AF3B81" Session-Id = "grump.example.

Diameter Base Protocol AVPs
The following table describes the Diameter AVPs defined in the base protocol. possible flag values and whether the AVP MAY be encrypted. Similarly.
Standards Track
[Page 53]
. redirect or relay) then the message MUST NOT be sent unless there is end-to-end security between the originator and the recipient or the originator has locally trusted configuration that indicates that end-to-end security is not needed.5. For the originator of a Diameter message.
Calhoun. redirect or relay) then the message MUST NOT be sent unless there is end-to-end security between the originator and the recipient and integrity / confidentiality protection is offered for this AVP OR the originator has locally trusted configuration that indicates that end-to-end security is not needed. Due to space constraints. their AVP Code values. a "P" in the "MAY" column means that if a message containing that AVP is to be sent via a Diameter agent (proxy. types. "Encr" (Encryption) means that if a message containing that AVP is to be sent via a Diameter agent (proxy.RFC 3588
Diameter Based Protocol
September 2003
4. for the originator of a Diameter message. et al. the short form DiamIdent is used to represent DiameterIdentity.

causing the transport connection to be shutdown. 2. When a peer is deemed suspect.
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[Page 56]
. it may not be economical to have an established connection to all of them. et al. and the connection to the peer is considered stabilized. and assume the role of either primary or secondary.2. while acting as a secondary for another realm. Typically. 5. no new requests should be forwarded to the peer. In the event the peer being removed is either the primary or secondary. the following mechanisms are described. implementations are free to load balance requests between a set of peers. The peer is no longer reachable. an alternate peer SHOULD replace the deleted peer. Note that a given peer MAY act as a primary for a given realm. but failover procedures are invoked. a node MAY have additional connections. any pending requests are sent to the secondary peer. Diameter Peer Discovery
Allowing for dynamic Diameter agent discovery will make it possible for simpler and more robust deployment of Diameter services.RFC 3588
Diameter Based Protocol
September 2003
5. These are based
Calhoun.
Peer Connections
Although a Diameter node may have many possible peers that it is able to communicate with. additional connections SHOULD be established to ensure that the necessary number of active connections exists.1. if it is deemed necessary. but in the event that failover procedures are invoked. Three watchdog messages are exchanged with accepted round trip times. At a minimum. When an active peer is moved to this mode. which could occur for various reasons.
Diameter Peers This section describes how Diameter nodes establish connections and communicate with peers.
5. known as the primary and secondary peers. Of course. including not receiving a DWA within an allotted timeframe. In order to promote interoperable implementations of Diameter peer discovery. all messages for a realm are sent to the primary peer. However. There are two ways that a peer is removed from the suspect peer list: 1. The peer is moved to the closed state. a Diameter node SHOULD have an established connection with two peers per realm.

each with a different service value. The second case is when a Diameter agent needs to discover another agent . As per RFC 2915 [NAPTR]. The Diameter implementation uses SLPv2 [SLP] to discover Diameter services. SLPv2 is discussed further in Appendix A. The Diameter implementation consults its list of static (manually) configured Diameter agent locations. The first is when a Diameter client needs to discover a first-hop Diameter agent. The resource record will contain an empty regular expression and a replacement value. This specification defines D2T for TCP and D2S for SCTP.1 The services relevant for the task of transport protocol selection are those with NAPTR service fields with values "AAA+D2x". We also establish an IANA registry for NAPTR service name to transport protocol mappings. The Diameter implementation has to know in advance which realm to look for a Diameter agent in. The first option (manual configuration) MUST be supported by all DIAMETER nodes. These NAPTR records provide a mapping from a domain. This could be deduced. where x is a letter that corresponds to a transport protocol supported by the domain. there will be multiple NAPTR records. In both cases. et al. The Diameter service template [TEMPLATE] is included in Appendix A. This is discussed further in Appendix A. 3. 3. the client
Calhoun.RFC 3588
Diameter Based Protocol
September 2003
on existing IETF standards.for further handling of a Diameter operation. which is the SRV record for that particular transport protocol. to the SRV record for contacting a server with the specific transport protocol in the NAPTR services field. from the ’realm’ in a NAI that a Diameter implementation needed to perform a Diameter operation on. It is recommended that SLPv2 security be deployed (this requires distributing keys to SLPv2 agents). If the server supports multiple transport protocols.
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[Page 57]
. for example. 2. while the latter two options (SRVLOC and DNS) MAY be supported. There are two cases where Diameter peer discovery may be performed. These will be used if they exist and respond. the following ’search order’ is recommended: 1. SLPv2 security SHOULD be used (requiring distribution of keys to SLPv2 agents) in order to ensure that discovered peers are authorized for their roles. The Diameter implementation performs a NAPTR query for a server in a particular realm.

For the purposes of this specification. et al. If a peer is discovered
Calhoun. 4. as well as an SRV record for the server. The domain suffixes in the NAPTR replacement field SHOULD match the domain of the original query. and the client could not validate that this was the desired behavior.RFC 3588
Diameter Based Protocol
September 2003
discards any records whose services fields are not applicable. AAAA RR’s or other similar records. Similarly. ’_diameter. If the DNS server returns no address records. and secured RRs may be included in the DNS. by configuration of a Diameter Server CA. the requester queries for those address records for the destination address. chosen according to the requestor’s network protocol capabilities. Authorization can be achieved for example.realm or ’_diameter. but this does not imply that it is authorized to act as a Diameter Server. 3. Authentication via IKE or TLS. the Diameter Peer MUST check to make sure that the discovered peers are authorized to act in its role. Alternatively this can be achieved by definition of OIDs within TLS or IKE certificates so as to signify Diameter Server authorization. the requestor gives up. Otherwise.2 A client MUST discard any service fields that identify a resolution service whose value is not "D2X".
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[Page 58]
.realm. for values of X that indicate transport protocols supported by the client. a web server may have obtained a valid TLS certificate. an attacker could modify the DNS records to contain replacement values in a different domain. For example. or the result of an attack Also. Note that entries created via DNS MUST expire (or be refreshed) within the DNS TTL. the domain name in the SRV query and the domain name in the target in the SRV record MUST both be valid based on the same site certificate. If the server is using a site certificate. Address records include A RR’s. The NAPTR processing as described in RFC 2915 will result in discovery of the most preferred transport protocol of the server that is supported by the client. several rules are defined._tcp’. If no NAPTR records are found. A dynamically discovered peer causes an entry in the Peer Table (see Section 2._sctp’. the domain name in the query and the domain name in the replacement field MUST both be valid based on the site certificate handed out by the server in the TLS or IKE exchange.6) to be created. or validation of DNS RRs via DNSSEC is not sufficient to conclude this.

This message allows the discovery of a peer’s identity and its capabilities (protocol version number. a successful CEA MAY be returned. the transport connection is closed. the lifetime of the peer entry is equal to the lifetime of the transport connection. or a CEA MAY be issued with the Result-Code AVP set to DIAMETER_UNKNOWN_PEER.
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. etc. it is still possible that an upstream agent receives a message for which it has no available peers to handle the application that corresponds to the Command-Code. a routing table entry (see Section 2. they MUST exchange the Capabilities Exchange messages.3.RFC 3588
Diameter Based Protocol
September 2003
outside of the local realm.7) for the peer’s realm is created. CERs received from unknown peers MAY be silently discarded. In such instances. and SHOULD disconnect the transport layer connection. Since the CER/CEA messages cannot be proxied.) The receiver only issues support for the Diameter Diameter node MUST cache ensure that unrecognized sent to a peer. 5. the ’E’ bit is set in the answer
Calhoun. security mechanisms. all the pending transactions destined to the unknown peer can be discarded. In case of a transport failure. as specified in the peer state machine (see Section 5. supported Diameter applications. A the supported applications in order to commands and/or AVPs are not unnecessarily
A receiver of a Capabilities-Exchange-Req (CER) message that does not have any applications in common with the sender MUST return a Capabilities-Exchange-Answer (CEA) with the Result-Code AVP set to DIAMETER_NO_COMMON_APPLICATION. Note that receiving a CER or CEA from a peer advertising itself as a Relay (see Section 2.4) MUST be interpreted as having common applications with the peer. If a CER from an unknown peer is answered with a successful CEA. In both cases. The routing table entry’s expiration MUST match the peer’s expiration value. The CER and CEA messages MUST NOT be proxied. Similarly. If the local policy permits receiving CERs from unknown hosts. Capabilities Exchange
When two Diameter peers establish a transport connection. commands to its peers that have advertised application that defines the command. redirected or relayed.6). a receiver of a Capabilities-Exchange-Req (CER) message that does not have any security mechanisms in common with the sender MUST return a Capabilities-Exchange-Answer (CEA) with the Result-Code AVP set to DIAMETER_NO_COMMON_SECURITY. et al. and SHOULD disconnect the transport layer connection.

. Diameter Header: 257. or a message with an application-specific command code.RFC 3588
Diameter Based Protocol
September 2003
message (see Section 7. Upon detection of a transport failure. indicated by the CommandCode set to 257 and the Command Flags’ ’R’ bit set.g. indicated by the Command-Code set to 257 and the Command Flags’ ’R’ bit cleared. is sent in response to a CER message. 5.
Calhoun. which allows for connections to span multiple interfaces and multiple IP addresses.1. With the exception of the Capabilities-Exchange-Request message. is sent to exchange local capabilities.2. Capabilities-Exchange-Request
The Capabilities-Exchange-Request (CER). REQ > Origin-Host } Origin-Realm } Host-IP-Address } Vendor-Id } Product-Name } Origin-State-Id ] Supported-Vendor-Id ] Auth-Application-Id ] Inband-Security-Id ] Acct-Application-Id ] Vendor-Specific-Application-Id ] Firmware-Revision ] AVP ]
Capabilities-Exchange-Answer
The Capabilities-Exchange-Answer (CEA). When Diameter is run over SCTP [SCTP]. MAY only be forwarded to a host that has explicitly advertised support for the application (or has advertised the Relay Application Identifier).
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[Page 60]
.3. Message Format <CER> ::= < { { 1* { { { [ * [ * [ * [ * [ * [ [ * [ 5. the Capabilities-Exchange-Request message MUST contain one Host-IPAddress AVP for each potential IP address that MAY be locally used when transmitting Diameter messages. et al.) with the Result-Code AVP set to DIAMETER_UNABLE_TO_DELIVER to inform the downstream to take action (e. re-routing request to an alternate peer).3. this message MUST NOT be sent to an alternate peer. a message of type Request that includes the Auth-Application-Id or Acct-Application-Id AVPs.

Firmware-Revision AVP
The Firmware-Revision AVP (AVP Code 267) is of type Unsigned32 and is used to inform a Diameter peer of the firmware revision of the issuing device.3.3.3. A Vendor-Id value of zero in the CER or CEA messages is reserved and indicates that this field is ignored.3.4. multiple IP addresses. et al. It is also envisioned that the combination of the Vendor-Id. Diameter Header: 257 > Result-Code } Origin-Host } Origin-Realm } Host-IP-Address } Vendor-Id } Product-Name } Origin-State-Id ] Error-Message ] Failed-AVP ] Supported-Vendor-Id ] Auth-Application-Id ] Inband-Security-Id ] Acct-Application-Id ] Vendor-Specific-Application-Id ] Firmware-Revision ] AVP ]
Vendor-Id AVP
The Vendor-Id AVP (AVP Code 266) is of type Unsigned32 and contains the IANA "SMI Network Management Private Enterprise Codes" [ASSIGNNO] value assigned to the vendor of the Diameter application. hence. In combination with the Supported-Vendor-Id AVP (Section 5.3.3. 5. the Capabilities-Exchange-Answer message MUST contain one Host-IP-Address AVP for each potential IP address that MAY be locally used when transmitting Diameter messages.4) AVPs MAY provide very useful debugging information. Message Format <CEA> ::= < { { { 1* { { { [ [ * [ * [ * [ * [ * [ * [ [ * [ 5.RFC 3588
Diameter Based Protocol
September 2003
When Diameter is run over SCTP [SCTP].7) and the Firmware-Revision (Section 5. which allows connections to span multiple interfaces.
Calhoun. Product-Name (Section 5.
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.6). this MAY be used in order to know which vendor specific attributes may be sent to the peer.

5. the peer may periodically attempt to reconnect.6. or that the peer has rebooted. the
Calhoun. The Disconnect-Peer-Request message is used by a Diameter node to inform its peer of its intent to disconnect the transport layer. Supported-Vendor-Id AVP
The Supported-Vendor-Id AVP (AVP Code 265) is of type Unsigned32 and contains the IANA "SMI Network Management Private Enterprise Codes" [ASSIGNNO] value assigned to a vendor other than the device vendor. message to be forwarded). its peer cannot know the reason for the disconnect.RFC 3588
Diameter Based Protocol
September 2003
For devices that do not have a firmware revision (general purpose computers running Diameter software modules. 5.5. In the event that the disconnect was a result of either a shortage of internal resources. This is used in the CER and CEA messages in order to inform the peer that the sender supports (a subset of) the vendor-specific AVPs defined by the vendor identified in this AVP. and contains the vendor assigned name for the product. as stated in Section 2.1. or simply that the node in question has no intentions of forwarding any Diameter messages to the peer in the foreseeable future.3. Upon receipt of the message. et al. 5. In these cases. All source addresses that a Diameter node expects to use with SCTP [SCTP] MUST be advertised in the CER and CEA messages by including a Host-IPAddress AVP for each address.3. the revision of the Diameter software module may be reported instead. Disconnecting Peer connections
When a Diameter node disconnects one of its transport connections. The Product-Name AVP SHOULD remain constant across firmware revisions for the same product.3.4.. a periodic connection request would not be welcomed. 5. Host-IP-Address AVP
The Host-IP-Address AVP (AVP Code 257) is of type Address and is used to inform a Diameter peer of the sender’s IP address.
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[Page 62]
. and will most likely assume that a connectivity problem occurred. This AVP MUST ONLY be used in the CER and CEA messages. The Disconnection-Reason AVP contains the reason the Diameter node issued the Disconnect-Peer-Request message. Product-Name AVP
The Product-Name AVP (AVP Code 269) is of type UTF8String.g.7. and that the peer shouldn’t reconnect unless it has a valid reason to do so (e. for instance).

1. which would otherwise cause a race condition. The receiver of the Disconnect-Peer-Answer initiates the transport disconnect. 5. which SHOULD contain an error if messages have recently been forwarded. the transport connection is shutdown. et al. Upon receipt of this message. is sent as a response to the Disconnect-Peer-Request message.
Disconnect-Peer-Answer
The Disconnect-Peer-Answer (DPA). The following values are supported:
Calhoun. Message Format <DPR> ::= < { { { Diameter Header: 282.RFC 3588
Diameter Based Protocol
September 2003
Disconnect-Peer-Answer is returned. this message MUST NOT be sent to an alternate peer.
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[Page 63]
. indicated by the Command-Code set to 282 and the Command Flags’ ’R’ bit cleared.4. REQ > Origin-Host } Origin-Realm } Disconnect-Cause }
5.2.4. Upon detection of a transport failure. is sent to a peer to inform its intentions to shutdown the transport connection. A Diameter node MUST include this AVP in the Disconnect-Peer-Request message to inform the peer of the reason for its intention to shutdown the transport connection. Message Format <DPA> ::= < { { { [ * [ Diameter Header: 282 > Result-Code } Origin-Host } Origin-Realm } Error-Message ] Failed-AVP ]
5.4. indicated by the Command-Code set to 282 and the Command Flags’ ’R’ bit set.3. Disconnect-Peer-Request
The Disconnect-Peer-Request (DPR).
Disconnect-Cause AVP
The Disconnect-Cause AVP (AVP Code 273) is of type Enumerated. and are likely in flight.

5.
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[Page 64]
. et al. this message MUST NOT be sent to an alternate peer. indicated by the Command-Code set to 280 and the Command Flags’ ’R’ bit set.3). is sent as a response to the Device-Watchdog-Request message. Upon detection of a transport failure. Transport Failure Detection
Given the nature of the Diameter protocol. and it has determined that the transport connection needs to be closed. The Device-Watchdog-Request and DeviceWatchdog-Answer messages.5. Message Format <DWR> ::= < { { [ Diameter Header: 280. and will provide better failover performance.5. are used to proactively detect transport failures. indicated by the Command-Code set to 280 and the Command Flags’ ’R’ bit cleared.
Device-Watchdog-Answer
The Device-Watchdog-Answer (DWA). it is recommended that transport failures be detected as soon as possible. resulting in unnecessary delays.1.5. Detecting such failures will minimize the occurrence of messages sent to unavailable agents. since it does not expect any messages to be exchanged in the near future.
Calhoun.2. is sent to a peer when no traffic has been exchanged between two peers (see Section 5.RFC 3588
Diameter Based Protocol
September 2003
REBOOTING 0 A scheduled reboot is imminent. BUSY 1 The peer’s internal resources are constrained. 5. defined in this section. DO_NOT_WANT_TO_TALK_TO_YOU 2 The peer has determined that it does not see a need for the transport connection to exist. REQ > Origin-Host } Origin-Realm } Origin-State-Id ]
5. Device-Watchdog-Request
The Device-Watchdog-Request (DWR). 5.

All Diameter implementations MUST support the algorithm defined in the specification in order to be compliant to the Diameter base protocol. Such an error requires that the agent return an answer message with the ’E’ bit set and the Result-Code AVP set to DIAMETER_UNABLE_TO_DELIVER.
Calhoun. In order for a Diameter node to perform failover procedures. On booting a Diameter client or agent. it is necessary for the node to maintain a pending message queue for a given peer.
Transport Failure Algorithm
The transport failure algorithm is defined in [AAATRANS]. if possible. It is important to note that multiple identical requests or answers MAY be received as a result of a failover. if possible all messages in the queue are sent to an alternate agent with the T flag set.
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. 5. An example of a case where it is not possible to forward the message to an alternate server is when the message has a fixed destination.5. This is commonly referred to as failover. the corresponding request is removed from the queue. et al. it is necessary for all pending request messages to be forwarded to an alternate agent. and the unavailable peer is the message’s final destination (see Destination-Host AVP). The End-to-End Identifier field in the Diameter header along with the Origin-Host AVP MUST be used to identify duplicate messages. Failover and Failback Procedures
In the event that a transport failure is detected with a peer. the T flag is also set on any records still remaining to be transmitted in non-volatile storage.5.RFC 3588
Diameter Based Protocol
September 2003
Message Format <DWA> ::= < { { { [ * [ [ Diameter Header: 280 > Result-Code } Origin-Host } Origin-Realm } Error-Message ] Failed-AVP ] Original-State-Id ]
5.3. When a transport failure is detected.4. The Hop-by-Hop Identifier field is used to match the answer with the queued request. When an answer message is received.

Note in particular that [AAATRANS] requires the use of watchdog messages to probe connections. as space requires. The lack of a prefix indicates that the event or action is the same regardless of the connection on which the event occurred. Peer State Machine
This section contains a finite state machine that MUST be observed by all Diameter implementations. as space requires.6. Once a connection has been successfully established. DWR and DWA messages are to be used. If the TLS handshake is successful. The stable states that a state machine may be in are Closed. both ends move to the closed state. and reopen transport connections. For TLS usage.is used to represent the initiator (connecting) connection. a TLS handshake will begin when both ends are in the open state. This state machine is closely coupled with the state machine described in [AAATRANS]. one of the two connections will shut down. I.
Calhoun. Note that I-Open and R-Open are equivalent except for whether the initiator or responder transport connection is used for communication. For Diameter. which is used to open. In the case of an election. probe. while the R.RFC 3588
Diameter Based Protocol
September 2003
As described in Section 2. failover. Multiple actions are separated by commas. and may continue on succeeding lines.
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[Page 66]
. The responder connection will survive if the Origin-Host of the local Diameter entity is higher than that of the peer. all other states are intermediate. all further messages will be sent via TLS. et al. A CER message is always sent on the initiating connection immediately after the connection request is successfully completed. Similarly. I-Open and R-Open.is used to represent the responder (listening) connection. 5. Note that the results of an election on one peer are guaranteed to be the inverse of the results on the other. close. The state machine constrains only the behavior of a Diameter implementation as seen by Diameter peers through events on the wire. All subsequent messages are sent on the surviving connection.1. If the handshake fails. a connection request should be periodically attempted with the failed peer in order to re-establish the transport connection. Each Diameter node MUST follow the state machine described below when communicating with each peer. This is commonly referred to as failback. messages can once again be forwarded to the peer. state and next state may also span multiple lines. the initiator connection will survive if the peer’s Origin-Host is higher.

Upon receipt of CER. in the general case. I-Snd-DWA Process-DWA R-Reject I-Snd-DPR I-Snd-DPA. Because handling of incoming connections up to and including receipt of CER requires logic. or if an implementation-defined timeout occurs prior to receipt of CER. the Origin-Host that identifies the peer is used to locate the state machine associated with that peer. The logic that handles incoming connections SHOULD close and discard the connection if any message other than CER arrives. it is described separately in this section rather than in the state machine above. and the source port of an incoming connection is arbitrary.RFC 3588
Diameter Based Protocol
September 2003
R-Peer-Disc R-Rcv-CER R-Rcv-CEA I-Open Send-Message I-Rcv-Message I-Rcv-DWR I-Rcv-DWA R-Conn-CER Stop I-Rcv-DPR I-Peer-Disc I-Rcv-CER I-Rcv-CEA Closing I-Rcv-DPA R-Rcv-DPA Timeout I-Peer-Disc R-Peer-Disc
R-Disc R-Snd-CEA Process-CEA I-Snd-Message Process Process-DWR.
Calhoun. possible to know the identity of that peer until a CER is received from it.
Incoming connections
When a connection request is received from a Diameter peer.1. a Diameter peer must employ logic separate from the state machine to receive connection requests. For this reason. it is not. Once CER arrives on a new connection. accept them. the identity of the connecting peer can be uniquely determined from Origin-Host. separate from that of any individual state machine associated with a particular peer.
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[Page 68]
. and the new connection and CER are passed to the state machine as an R-Conn-CER event.6. This is because host and port determine the identity of a Diameter peer. et al. and await CER. I-Disc I-Disc I-Snd-CEA Process-CEA I-Disc R-Disc Error I-Disc R-Disc
Closed R-Open R-Open I-Open I-Open I-Open I-Open I-Open Closing Closed Closed I-Open I-Open Closed Closed Closed Closed Closed
5.

A message other than CER. and the local node was the winner.6. A positive acknowledgement is received confirming that the transport connection is established.
Events
Transitions and actions in the automaton are caused by events. but would occur on one of two possible connections.g. on system shutdown). et al. An election was held. A negative acknowledgement was received stating that the transport connection was not established. DPA. A message is to be sent.. CEA. since the actual event would be identical. A DPR message from the peer was received. DPR. A DPA message from the peer was received. and the associated CER has arrived. In this section. A CEA message from the peer was received. we will ignore the -I and -R prefix.2. A disconnection indication from the peer was received.RFC 3588
Diameter Based Protocol
September 2003
5.
R-Conn-CER
Rcv-Conn-Ack
Rcv-Conn-Nack
Timeout
Rcv-CER Rcv-CEA Rcv-Non-CEA Peer-Disc Rcv-DPR Rcv-DPA Win-Election
Send-Message Rcv-Message
Stop
Calhoun. DWR or DWA was received. Start The Diameter application has signaled that a connection should be initiated with the peer. An application-defined timer has expired while waiting for some event. An acknowledgement is received stating that the transport connection has been established.
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[Page 69]
. A CER message from the peer was received. A message other than CEA from the peer was received. The Diameter application has signaled that a connection should be terminated (e.

et al. A received CEA is processed.and R-prefix. either politely or abortively.
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[Page 70]
. In this section we will ignore the I.3. and any local resources are freed. A DWR message is sent. and local resources are freed.RFC 3588
Diameter Based Protocol
September 2003
5. in response to an error condition.6.6. The DWR message is serviced. but would occur on one of two possible connections.
Actions
Actions in the automaton are caused by events and typically indicate the transmission of packets and/or an action to be taken on the connection. The CER associated with the R-Conn-CER is processed. The incoming connection associated with the R-Conn-CER is accepted as the responder connection. Local resources are freed. The transport layer connection is disconnected. since the actual action would be identical. A CEA message is sent to the peer. A CER message is sent to the peer. A DPR message is sent to the peer. A DWA message is sent. A message is sent. If necessary.4 for more information). An election occurs (see Section 5. A DPA message is sent to the peer. Snd-Conn-Req Accept A transport connection is initiated with the peer. The transport layer connection is disconnected. the connection is shutdown.
Reject
Process-CER Snd-CER Snd-CEA Cleanup
Error
Process-CEA Snd-DPR Snd-DPA Disc
Elect
Snd-Message Snd-DWR Snd-DWA Process-DWR
Calhoun. The incoming connection associated with the R-Conn-CER is disconnected.

4. a request that needs to be sent to a home server serving a specific realm. otherwise. Diameter message processing This section describes how Diameter requests and answers are created and processed. in one of these three combinations: a request that is not able to be proxied (such as CER) MUST NOT contain either Destination-Realm or Destination-Host AVPs. 6.
Calhoun.RFC 3588
Diameter Based Protocol
September 2003
Process-DWA Process 5. but not to a specific server (such as the first request of a series of round-trips).
The DWA message is serviced. If the local Diameter entity’s Origin-Host is higher than the peer’s. The comparison proceeds by considering the shorter OctetString to be padded with zeros so that it length is the same as the length of the longer. MUST contain both the Destination-Realm and Destination-Host AVPs. a request that needs to be sent to a specific home server among those serving a given realm. 6.1.6. et al. then performing an octet-by-octet unsigned comparison with the first octet being most significant. but MUST NOT contain a Destination-Host AVP.
-
-
The Destination-Host AVP is used as described above when the destination of the request is fixed. MUST contain a DestinationRealm AVP. A message is serviced. Diameter Request Routing Overview
A request is sent towards its final destination using a combination of the Destination-Realm and Destination-Host AVPs.
The Election Process
The election is performed on the responder. Any remaining octets are assumed to have value 0x80. a Win-Election event is issued locally. which includes: Authentication requests that span multiple round trips A Diameter message that uses a security mechanism that makes use of a pre-established session key shared between the source and the final destination of the message. The responder compares the Origin-Host received in the CER sent by its peer with its own Origin-Host.
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[Page 71]
.

Note that an agent can forward a request to a host described in the Destination-Host AVP only if the host in question is included in its peer table (see Section 2. Request messages that may be forwarded by Diameter agents (proxies.g. an Auth-Application-Id AVP or a Vendor-SpecificApplication-Id AVP. with the E-bit set.1. A message that MUST NOT be forwarded by Diameter agents (proxies.RFC 3588
Diameter Based Protocol
September 2003
-
Server initiated messages that MUST be received by a specific Diameter client (e. Otherwise. an answer is returned with the Result-Code set to DIAMETER_UNABLE_TO_DELIVER. access device).1. 2.5 are followed. See Section 7 for more detail on error handling. such as the Abort-SessionRequest message.. If the message is intended for a Diameter peer with whom the local host is able to directly communicate. For routing of Diameter messages to work within an administrative domain.
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[Page 72]
. the procedures listed in Section 6. If none of the above is successful.
Calhoun. the message is processed in the following order: 1.1. 4. The value of the Destination-Realm AVP MAY be extracted from the User-Name AVP. The Destination-Realm AVP MUST be present if the message is proxiable.7). and still comply with the protocol specification. which is known as Request Routing.1. 3. et al.6 are followed. This is known as Request Forwarding. redirects or relays) MUST also contain an AcctApplication-Id AVP. redirects or relays) MUST not include the Destination-Realm in its ABNF.6). Note the processing rules contained in this section are intended to be used as general guidelines to Diameter developers. If the message is destined for the local host.4 are followed. Certain implementations MAY use different methods than the ones described here. or other applicationspecific methods. the procedures listed in Section 6. the request is routed based on the Destination-Realm only (see Sections 6. The procedures listed in Section 6. which is used to request that a particular user’s session be terminated. When a message is received. all Diameter nodes within the realm MUST be peers.

When such an event occurs.RFC 3588
Diameter Based Protocol
September 2003
6. the following procedures MUST be followed: the Hop-by-Hop Identifier should be set to a locally unique value The message should be saved in the list of pending requests.2. an Auth-Application-Id or a VendorSpecific-Application-Id AVP must be included if the request is proxiable. or as the result of a forwarding or routing operation. originated either locally. in addition to any other procedures described in the application definition for that specific request. et al. 6.1. an Acct-Application-Id AVP. Sending a Request
-
-
6. A loop is detected if the server finds its own identity in a Route-Record AVP.1.1. the agent MUST answer with the Result-Code AVP set to DIAMETER_LOOP_DETECTED.
Calhoun.
Other actions to perform on the message based on the particular role the agent is playing are described in the following sections. Receiving Requests
A relay or proxy agent MUST check for forwarding loops when receiving requests. used to identify the source of the message the Destination-Host and Destination-Realm AVPs MUST be set to the appropriate values as described in Section 6.3.1.
Originating a Request
When creating a request. 6. the following procedures MUST be followed: the Command-Code is set to the appropriate value the ’R’ bit is set the End-to-End Identifier is set to a locally unique value the Origin-Host and Origin-Realm AVPs MUST be set to the appropriate values.
When sending a request.4. Processing Local Requests
A request is known to be for local consumption when one of the following conditions occur: The Destination-Host AVP contains the local host’s identity.
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.1.1.

Diameter agents MAY have a list of locally supported realms and applications. Acct-Application-Id or Vendor-SpecificApplication-Id.2 should be used to generate the corresponding answer.
Calhoun. and the host encoded in the DestinationHost AVP is one that is present in the peer table.1. The Diameter peer table contains all of the peers that the local node is able to directly communicate with. the Destination-Realm AVP contains a realm the server is configured to process locally. et al. the message is routed to the peer configured in the Realm Routing Table (see Section 2.1. the rules in Section 6.7). and the Diameter application is locally supported. The realm MAY be retrieved from the User-Name AVP. or Both the Destination-Host and the Destination-Realm are not present. Each of the servers associated with the routing entry are added in separate Redirect-Host AVP.
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[Page 74]
. the message SHOULD be forwarded to the peer.
-
When a request is locally processed.5. The realm portion of the NAI is inserted in the Destination-Realm AVP. A Diameter message that may be forwarded by Diameter agents (proxies. which is in the form of a Network Access Identifier (NAI). and include the Result-Code AVP to DIAMETER_REDIRECT_INDICATION. Request Forwarding
Request forwarding is done using the Diameter Peer Table.1. Redirecting requests
When a redirect agent receives a request whose routing entry is set to REDIRECT. while maintaining the Hop-by-Hop Identifier in the header. 6.7.RFC 3588
Diameter Based Protocol
September 2003
-
The Destination-Host AVP is not present. it MUST reply with an answer message with the ’E’ bit set. and MAY have a list of externally supported realms and applications. Request Routing
Diameter request message routing is done via realms and applications. 6. 6.6. When a request is received. redirects or relays) MUST include the target realm in the Destination-Realm AVP and one of the application identification AVPs Auth-Application-Id. When a request is received that includes a realm and/or application that is not locally supported.

Proxy-Info AVP has certain security implications and SHOULD contain an embedded HMAC with a node-local key. The AVP contains the identity of the peer the request was received from.com |------------->| example.3) that is to be redirected. which includes the IP address. Relaying and Proxying Requests
A relay or proxy agent MUST append a Route-Record AVP to all requests forwarded.com | | DIAMETER_REDIRECT_INDICATION + | | Redirect-Host AVP(s) | v +-------------+ 3. and the Result-Code AVP set to DIAMETER_REDIRECT_INDICATION uses the hop-byhop field in the Diameter header to identify the request in the pending message queue (see Section 5. Alternatively. The message is then forwarded to the next hop. as identified in the Realm Routing Table. et al. it MAY simply use local storage to store state information. and replaced with a locally unique value.1. A relay or proxy agent MAY include the Proxy-Info AVP in requests if it requires access to any local state information when the corresponding response is received. The Hop-by-Hop identifier in the request is saved. port and protocol.net | | Relay | | Diameter | | Agent |<-------------| Server | +-------------+ 4. Request | | Result-Code = joe@example. The source of the request is also saved. and the request is sent directly to it. one is created. Multiple Redirect-Host AVPs are allowed. command + ’E’ bit 1. The receiver of the answer message with the ’E’ bit set selects exactly one of these hosts as the destination of the redirected message. 6. Request +-------------+ | example. If no transport connection exists with the new agent.
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[Page 75]
.8.
Calhoun.RFC 3588
Diameter Based Protocol
September 2003
+------------------+ | Diameter | | Redirect Agent | +------------------+ ^ | 2. Answer +-------------+ Figure 5: Diameter Redirect Agent The receiver of the answer message with the ’E’ bit set.

net) (Origin-Realm=mno.net) (Destination-Realm=example.net) +------+ ------> +------+ ------> +------+ | | (Request) | | (Request) | | | NAS +-------------------+ DRL +-------------------+ HMS | | | | | | | +------+ <-----+------+ <-----+------+ example. The same End-to-End identifier in the request is used in the answer. The ’P’ bit is set to the same value as the one in the request.mno. in addition to any additional procedures that MAY be discussed in the Diameter application defining the command: The same Hop-by-Hop identifier in the request is used in the answer.2.example. Diameter Answer Processing
When a request is locally processed.example.com) (DestinationRealm=example. it MUST be included in the answer.net (Answer) example. the following procedures MUST be applied to create the associated answer.com) (Origin-Realm=example.com) (Origin-Realm=example.com (Origin-Host=hms.RFC 3588
Diameter Based Protocol
September 2003
Figure 6 provides an example of message routing using the procedures listed in these sections. The local host’s identity is encoded in the Origin-Host AVP.net) (Origin-Realm=mno.net (Answer) example.
-
-
-
-
-
Calhoun.mno.example. in the same order they were present in the request.com) (Route-Record=nas. (Origin-Host=nas.net) (Origin-Host=nas.com) (Origin-Host=hms. et al.
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[Page 76]
.com) Figure 6: Routing of Diameter messages 6. The Result-Code AVP is added with its value indicating success or failure. If the Session-Id is present in the request. The Destination-Host and Destination-Realm AVPs MUST NOT be present in the answer message. Any Proxy-Info AVPs in the request MUST be added to the answer message.

Relaying and Proxying Answers
If the answer is for a request which was proxied or relayed.3. The corresponding message should be removed from the list of pending requests. Any additional local errors detected SHOULD be logged. Processing received Answers
A Diameter client or proxy MUST match the Hop-by-Hop Identifier in an answer received against the list of pending requests. Relay agents MUST NOT modify this AVP. 6.2. the agent MUST restore the original value of the Diameter header’s Hopby-Hop Identifier field. it MUST modify the Result-Code AVP to contain the appropriate error in the message destined towards the access device as well as include the Error-Reporting-Host AVP and it MUST issue an STR on behalf of the access device. The value of the Origin-Host AVP is guaranteed to be unique within a single host. If the agent receives an answer message with a Result-Code AVP indicating success. 6. but not reflected in the Result-Code AVP.1.3) are also subjected to the above processing rules. If the last Proxy-Info AVP in the message is targeted to the local Diameter server. and MUST be present in all Diameter messages. If a relay or proxy agent receives an answer with a Result-Code AVP indicating a failure.2. Note that the Origin-Host AVP may resolve to more than one address as the Diameter peer may support more than one address. the AVP MUST be removed before the answer is forwarded.2.RFC 3588
Diameter Based Protocol
September 2003
Note that the error messages (see Section 7.
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[Page 77]
. it MUST NOT modify the contents of the AVP. This AVP identifies the endpoint that originated the Diameter message. Origin-Host AVP
The Origin-Host AVP (AVP Code 264) is of type DiameterIdentity. et al. 6. It SHOULD ignore answers received that do not match a known Hop-by-Hop Identifier. and it wishes to modify the AVP to indicate an error.
Calhoun. The agent MUST then send the answer to the host that it received the original request from.

7. and MUST NOT be present in Answer messages. This AVP MUST be present in all unsolicited agent initiated messages.
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[Page 78]
. This AVP SHOULD be placed as close to the Diameter header as possible. and contains the realm the message is to be routed to. Request messages whose ABNF does not list the Destination-Realm AVP as a mandatory AVP are inherently non-routable messages. Diameter servers initiating a request message use the value of the Origin-Realm AVP from a previous message received from the intended target host (unless it is known a priori). and therefore MUST NOT be protected by end-to-end security. This AVP contains the Realm of the originator of any Diameter message and MUST be present in all messages.6. 6. These AVPs change as Diameter messages are processed by agents. Diameter Clients insert the realm portion of the User-Name AVP. Destination-Realm AVP
The Destination-Realm AVP (AVP Code 283) is of type DiameterIdentity. The Destination-Realm AVP MUST NOT be present in Answer messages. Origin-Realm AVP
The Origin-Realm AVP (AVP Code 296) is of type DiameterIdentity. Destination-Host AVP
The Destination-Host AVP (AVP Code 293) is of type DiameterIdentity.4.RFC 3588
Diameter Based Protocol
September 2003
This AVP SHOULD be placed as close to the Diameter header as possible. This AVP SHOULD be placed as close to the Diameter header as possible. Routing AVPs
The AVPs defined in this section are Diameter AVPs used for routing purposes. et al.10 6. the Destination-Realm AVP is used to perform message routing decisions. 6.5. 6. The absence of the Destination-Host AVP will cause a message to be sent to any Diameter server supporting the application within the realm specified in Destination-Realm AVP. 6. MAY be present in request messages. This AVP SHOULD be placed as close to the Diameter header as possible.
Calhoun. When present.

Route-Record AVP
The Route-Record AVP (AVP Code 282) is of type DiameterIdentity.7.
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[Page 79]
. Proxy-State AVP
The Proxy-State AVP (AVP Code 33) is of type OctetString. 6.8. Proxy-Info AVP The Grouped
The Proxy-Info AVP (AVP Code 284) is of type Grouped.3.4).2. This AVP contains the identity of the host that added the Proxy-Info AVP.7. Acct-Application-Id AVP
The Acct-Application-Id AVP (AVP Code 259) is of type Unsigned32 and is used in order to advertise support of the Accounting portion of an application (see Section 2.4). The identity added in this AVP MUST be the same as the one received in the Origin-Host of the Capabilities Exchange message.10. et al.4. 6. Data field has the following ABNF grammar: Proxy-Info ::= < { { * [ 6. and contains state local information. and MUST be treated as opaque data.9. Exactly one of the AuthApplication-Id and Acct-Application-Id AVPs MAY be present. Auth-Application-Id AVP
The Auth-Application-Id AVP (AVP Code 258) is of type Unsigned32 and is used in order to advertise support of the Authentication and Authorization portion of an application (see Section 2.1. The Acct-Application-Id MUST also be present in all Accounting messages.
Calhoun. Inband-Security-Id AVP
The Inband-Security-Id AVP (AVP Code 299) is of type Unsigned32 and is used in order to advertise support of the Security portion of the application.7.RFC 3588
Diameter Based Protocol
September 2003
6. The Auth-Application-Id MUST also be present in all Authentication and/or Authorization messages that are defined in a separate Diameter specification and have an Application ID assigned. 6.7. Proxy-Host AVP AVP Header: 284 > Proxy-Host } Proxy-State } AVP ]
The Proxy-Host AVP (AVP Code 280) is of type DiameterIdentity. 6. 6.

Redirect-Host-Usage AVP
The Redirect-Host-Usage AVP (AVP Code 261) is of type Enumerated.13.12. Redirect-Host AVP AVP Header: 260 > Vendor-Id ] Auth-Application-Id } Acct-Application-Id }
One or more of instances of this AVP MUST be present if the answer message’s ’E’ bit is set and the Result-Code AVP is set to DIAMETER_REDIRECT_INDICATION. 6. This AVP SHOULD be placed as close to the Diameter header as possible. et al. TLS 1 This node supports TLS security. This AVP MAY be present in answer messages whose ’E’ bit is set and the Result-Code AVP is set to DIAMETER_REDIRECT_INDICATION. AVP Format <Vendor-Specific-Application-Id> ::= < 1* [ 0*1{ 0*1{ 6. the following values are supported.
Calhoun. but there is ample room to add new security Ids. if the AVP is omitted.RFC 3588
Diameter Based Protocol
September 2003
Currently. Exactly one of the Auth-Application-Id and Acct-Application-Id AVPs MAY be present. the receiving Diameter node SHOULD forward the request directly to one of the hosts identified in these AVPs. Upon receiving the above. This is the default value.
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. Vendor-Specific-Application-Id AVP
6.
The Vendor-Specific-Application-Id AVP (AVP Code 260) is of type Grouped and is used to advertise support of a vendor-specific Diameter Application. as defined by [TLS]. The server contained in the selected Redirect-Host AVP SHOULD be used for all messages pertaining to this session. This AVP MUST also be present as the first AVP in all experimental commands defined in the vendor-specific application. NO_INBAND_SECURITY 0 This peer does not support TLS.11.

any associated peer and routing table entries MUST be deleted. Note that once a host created due to a redirect indication is no longer reachable. this AVP dictates how the routing entry resulting from the Redirect-Host is to be used.
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[Page 81]
.
Calhoun. The following values are supported: DONT_CACHE 0 The host specified in the Redirect-Host AVP should not be cached.14. This is the default value. This AVP contains the maximum number of seconds the peer and route table entries.RFC 3588
Diameter Based Protocol
September 2003
When present. This AVP MUST be present in answer messages whose ’E’ bit is set. will be cached. ALL_SESSION 1 All messages within the same session. ALL_APPLICATION 4 All messages for the application requested MAY be sent to the host specified in the Redirect-Host AVP. Redirect-Max-Cache-Time AVP
The Redirect-Max-Cache-Time AVP (AVP Code 262) is of type Unsigned32. the Result-Code AVP is set to DIAMETER_REDIRECT_INDICATION and the Redirect-Host-Usage AVP set to a non-zero value. et al. as defined by the same value of the Session-ID AVP MAY be sent to the host specified in the Redirect-Host AVP. ALL_HOST 5 All messages that would be sent to the host that generated the Redirect-Host MAY be sent to the host specified in the RedirectHost AVP. REALM_AND_APPLICATION 3 All messages for the application requested to the realm specified MAY be sent to the host specified in the Redirect-Host AVP. ALL_REALM 2 All messages destined for the realm requested MAY be sent to the host specified in the Redirect-Host AVP. ALL_USER 6 All messages for the user requested MAY be sent to the host specified in the Redirect-Host AVP. created as a result of the Redirect-Host. 6.

For each end-to-end peer with which a node communicates (or remembers communicating) a different nonce value MUST be used and the counter is initiated at zero and increases by one each time this AVP is emitted to that peer.
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[Page 82]
. Given that this error falls
Calhoun.. As the answer is sent back towards the originator of the request. Application errors.
E2E-Sequence AVP
The E2E-Sequence AVP (AVP Code 300) provides anti-replay protection for end to end messages and is of type grouped.g. on the other hand.g. et al. 1. Error Handling There are two different types of errors in Diameter. Request |Diameter | +--------+ +-------------------->| | ^ | Relay 3 |-----------+ +---------+ Figure 7: Example of Protocol Error causing answer message
Figure 7 provides an example of a message forwarded upstream by a Diameter relay. and it detects that it cannot forward the request to the home server. answer + ’E’ set | Relay 2 | +--------+ |Diameter |<-+ (Unable to Forward) +---------+ |Diameter| | | | Home | | Relay 1 |--+ +---------+ | Server | +---------+ | 3. Request +---------+ Link Broken +-------------------------->|Diameter |----///----+ | +---------------------| | v +------+--+ | 2. generally occur due to a problem with a function specified in a Diameter application (e..RFC 3588
Diameter Based Protocol
September 2003
6. When a request message is received that causes a protocol error. When the message is received by Relay 2..15. an answer message is returned with the ’E’ bit set and the Result-Code AVP set to DIAMETER_UNABLE_TO_DELIVER. A protocol error is one that occurs at the base protocol level. protocol and application errors. CMS signing or encryption). Result-Code AVP values that are used to report protocol errors MUST only be present in answer messages whose ’E’ bit is set.g. This AVP MUST be included in all messages which use end-to-end protection (e. message routing error). Missing AVP). each proxy or relay agent MAY take action on the message. It contains a random value (an OctetString with a nonce) and counter (an Integer). an answer message is returned with the ’E’ bit set. and the Result-Code AVP is set to the appropriate protocol error value. 7. and MAY require per hop attention (e. user authentication.

yet is mandatory according to the command’s ABNF.
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. In these cases. Examples are: An unrecognized AVP is received with the ’M’ bit (Mandatory bit) set. Answer +---------+ (Missing AVP) (Missing AVP) Figure 8: Example of Application Error Answer message Figure 8 provides an example of a Diameter message that caused an application error. The receiver issues an answer with the Result-Code set to DIAMETER_MISSING_AVP. When application errors occur. with the Failed-AVP AVP containing the AVP causing the error.RFC 3588
Diameter Based Protocol
September 2003
within the protocol error category. and creates an AVP with the AVP Code and other fields set as expected in the missing AVP.
-
-
The Result-Code AVP describes the error that the Diameter node encountered in its processing. Request +---------+ 2. A command is received with an AVP that is omitted. Answer +---------+ 3. The created AVP is then added to the FailedAVP AVP. There are certain Result-Code AVP application errors that require additional AVPs to be present in the answer. causes an answer to be sent with the Result-Code AVP set to DIAMETER_AVP_UNSUPPORTED. attempt to route the message through its alternate Relay 3. the Diameter node MUST report only the first error it encountered
Calhoun. and given the error. et al. Request +---------+ | Access |------------>|Diameter |------------>|Diameter | | | | | | Home | | Device |<------------| Relay |<------------| Server | +---------+ 4. and the Failed-AVP AVP containing the offending AVP. the Diameter node that sets the Result-Code AVP to indicate the error MUST add the AVPs. An AVP that is received with an unrecognized value causes an answer to be returned with the Result-Code AVP set to DIAMETER_INVALID_AVP_VALUE. and adds the Result-Code AVP with the proper value. Application errors do not require any proxy or relay agent involvement. Relay 1 would take special action. and therefore the message would be forwarded back to the originator of the request. +---------+ 1. In case there are multiple errors. the Diameter entity reporting the error clears the ’R’ bit in the Command Flags.

2. DIAMETER_MULTI_ROUND_AUTH 1001 This informational error is returned by a Diameter server to inform the access device that the authentication mechanism being used requires multiple round trips. The Result-Code data field contains an IANA-managed 32-bit address space representing errors (see Section 11. All Diameter answer messages defined in IETF applications MUST include one Result-Code AVP. all identified by the thousands digit in the decimal notation: 1xxx 2xxx 3xxx 4xxx 5xxx (Informational) (Success) (Protocol Errors) (Transient Failures) (Permanent Failure)
A non-recognized class (one whose first digit is not defined in this section) MUST be handled as a permanent failure.1. Result-Code AVP
The Result-Code AVP (AVP Code 268) is of type Unsigned32 and indicates whether a particular request was completed successfully or whether an error occurred.1. DIAMETER_SUCCESS 2001 The Request was successfully completed. The specific errors that can be described by this AVP are described in the following section. and a subsequent request needs to be issued in order for access to be granted. 7. 7. et al.4).
Calhoun.
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. and additional action is required on its part before access is granted. Diameter provides the following classes of errors. 7.1.1.RFC 3588
Diameter Based Protocol
September 2003
(detected possibly in some implementation dependent order). A non-successful Result-Code AVP (one containing a non 2xxx value other than DIAMETER_REDIRECT_INDICATION) MUST include the Error-Reporting-Host AVP if the host setting the Result-Code AVP is different from the identity encoded in the Origin-Host AVP. Informational
Errors that fall within this category are used to inform the requester that a request could not be satisfied. Success
Errors that fall within the Success category are used to inform a peer that a request has been successfully completed.

DIAMETER_UNABLE_TO_DELIVER 3002 This error is given when Diameter can not deliver the message to the destination. the request was successfully completed. and it cannot provide the requested service. DIAMETER_REDIRECT_INDICATION 3006 A redirect agent has determined that the request could not be satisfied locally and the initiator of the request should direct the request directly to the server. if it is possible.
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. Note that these and only these errors MUST only be used in answer messages whose ’E’ bit is set. if one is available. but the peer reporting the error has identified a configuration problem.1. The message MAY be sent to an alternate peer. This MUST be used when a Diameter node receives an experimental command that it does not understand. whose contact information has been added to the response.RFC 3588
Diameter Based Protocol
September 2003
DIAMETER_LIMITED_SUCCESS 2002 When returned. DIAMETER_TOO_BUSY 3004 When returned. the Redirect-Host AVP MUST be present. but additional processing is required by the application in order to provide service to the user.3. either because no host within the realm supporting the required application was available to process the request. or because Destination-Host AVP was given without the associated Destination-Realm AVP. et al.
Calhoun. DIAMETER_LOOP_DETECTED 3005 An agent detected a loop while trying to get the message to the intended recipient. Protocol Errors
Errors that fall within the Protocol Error category SHOULD be treated on a per-hop basis. a Diameter node SHOULD attempt to send the message to an alternate peer. DIAMETER_REALM_NOT_SERVED 3003 The intended realm of the request is not recognized. and Diameter proxies MAY attempt to correct the error. This error MUST only be used when a specific server is requested. When set. DIAMETER_APPLICATION_UNSUPPORTED 3007 A request was sent for an application that is not supported. DIAMETER_COMMAND_UNSUPPORTED 3001 The Request contained a Command-Code that the receiver did not recognize or support. 7.

or that is inconsistent with the AVP’s definition. but MAY be able to satisfy the request in the future. DIAMETER_OUT_OF_SPACE 4002 A Diameter node received the accounting request but was unable to commit it to stable storage due to a temporary lack of space.RFC 3588
Diameter Based Protocol
September 2003
DIAMETER_INVALID_HDR_BITS 3008 A request was received whose bits in the Diameter header were either set to an invalid combination. ELECTION_LOST 4003 The peer has determined that it has lost the election process and has therefore disconnected the transport connection. 7. Permanent Failures Errors that fall within the permanent failures category are used to inform the peer that the request failed. DIAMETER_INVALID_AVP_BITS 3009 A request was received that included an AVP whose flag bits are set to an unrecognized value.5. DIAMETER_AUTHENTICATION_REJECTED 4001 The authentication process for the user failed. et al.1. DIAMETER_UNKNOWN_SESSION_ID 5002 The request contained an unknown Session-Id.
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. most likely due to an invalid password used by the user. Further attempts MUST only be tried after prompting the user for a new password.4.1. DIAMETER_UNKNOWN_PEER 3010 A CER was received from an unknown peer. and should not be attempted again.
Calhoun. 7. DIAMETER_AVP_UNSUPPORTED 5001 The peer received a message that contained an AVP that is not recognized or supported and was marked with the Mandatory bit. A Diameter message with this error MUST contain one or more FailedAVP AVP containing the AVPs that caused the failure. Transient Failures Errors that fall within the transient failures category are used to inform a peer that the request could not be satisfied at the time it was received. or to a value that is inconsistent with the command code’s definition.

RFC 3588

Diameter Based Protocol

September 2003

DIAMETER_AUTHORIZATION_REJECTED 5003 A request was received for which the user could not be authorized. This error could occur if the service requested is not permitted to the user. DIAMETER_INVALID_AVP_VALUE 5004 The request contained an AVP with an invalid value in its data portion. A Diameter message indicating this error MUST include the offending AVPs within a Failed-AVP AVP. DIAMETER_MISSING_AVP 5005 The request did not contain an AVP that is required by the Command Code definition. If this value is sent in the Result-Code AVP, a Failed-AVP AVP SHOULD be included in the message. The Failed-AVP AVP MUST contain an example of the missing AVP complete with the Vendor-Id if applicable. The value field of the missing AVP should be of correct minimum length and contain zeroes. DIAMETER_RESOURCES_EXCEEDED 5006 A request was received that cannot be authorized because the user has already expended allowed resources. An example of this error condition is a user that is restricted to one dial-up PPP port, attempts to establish a second PPP connection. DIAMETER_CONTRADICTING_AVPS 5007 The Home Diameter server has detected AVPs in the request that contradicted each other, and is not willing to provide service to the user. One or more Failed-AVP AVPs MUST be present, containing the AVPs that contradicted each other. DIAMETER_AVP_NOT_ALLOWED 5008 A message was received with an AVP that MUST NOT be present. Failed-AVP AVP MUST be included and contain a copy of the offending AVP.

The

DIAMETER_AVP_OCCURS_TOO_MANY_TIMES 5009 A message was received that included an AVP that appeared more often than permitted in the message definition. The Failed-AVP AVP MUST be included and contain a copy of the first instance of the offending AVP that exceeded the maximum number of occurrences DIAMETER_NO_COMMON_APPLICATION 5010 This error is returned when a CER message is received, and there are no common applications supported between the peers. DIAMETER_UNSUPPORTED_VERSION 5011 This error is returned when a request was received, whose version number is unsupported.

Calhoun, et al.

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RFC 3588

Diameter Based Protocol

September 2003

DIAMETER_UNABLE_TO_COMPLY 5012 This error is returned when a request is rejected for unspecified reasons. DIAMETER_INVALID_BIT_IN_HEADER 5013 This error is returned when an unrecognized bit in the Diameter header is set to one (1). DIAMETER_INVALID_AVP_LENGTH 5014 The request contained an AVP with an invalid length. A Diameter message indicating this error MUST include the offending AVPs within a Failed-AVP AVP. DIAMETER_INVALID_MESSAGE_LENGTH 5015 This error is returned when a request is received with an invalid message length. DIAMETER_INVALID_AVP_BIT_COMBO 5016 The request contained an AVP with which is not allowed to have the given value in the AVP Flags field. A Diameter message indicating this error MUST include the offending AVPs within a Failed-AVP AVP. DIAMETER_NO_COMMON_SECURITY 5017 This error is returned when a CER message is received, and there are no common security mechanisms supported between the peers. A Capabilities-Exchange-Answer (CEA) MUST be returned with the Result-Code AVP set to DIAMETER_NO_COMMON_SECURITY. 7.2. Error Bit

The ’E’ (Error Bit) in the Diameter header is set when the request caused a protocol-related error (see Section 7.1.3). A message with the ’E’ bit MUST NOT be sent as a response to an answer message. Note that a message with the ’E’ bit set is still subjected to the processing rules defined in Section 6.2. When set, the answer message will not conform to the ABNF specification for the command, and will instead conform to the following ABNF:

Note that the code used in the header is the same than the one found in the request message, but with the ’R’ bit cleared and the ’E’ bit set. The ’P’ bit in the header is set to the same value as the one found in the request message. 7.3. Error-Message AVP

The Error-Message AVP (AVP Code 281) is of type UTF8String. It MAY accompany a Result-Code AVP as a human readable error message. The Error-Message AVP is not intended to be useful in real-time, and SHOULD NOT be expected to be parsed by network entities. 7.4. Error-Reporting-Host AVP

The Error-Reporting-Host AVP (AVP Code 294) is of type DiameterIdentity. This AVP contains the identity of the Diameter host that sent the Result-Code AVP to a value other than 2001 (Success), only if the host setting the Result-Code is different from the one encoded in the Origin-Host AVP. This AVP is intended to be used for troubleshooting purposes, and MUST be set when the ResultCode AVP indicates a failure. 7.5. Failed-AVP AVP

The Failed-AVP AVP (AVP Code 279) is of type Grouped and provides debugging information in cases where a request is rejected or not fully processed due to erroneous information in a specific AVP. The value of the Result-Code AVP will provide information on the reason for the Failed-AVP AVP. The possible reasons for this AVP are the presence of an improperly constructed AVP, an unsupported or unrecognized AVP, an invalid AVP value, the omission of a required AVP, the presence of an explicitly excluded AVP (see tables in Section 10), or the presence of two or more occurrences of an AVP which is restricted to 0, 1, or 0-1 occurrences.

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The second only makes use of accounting.6. and can optionally make use of accounting. All Diameter answer messages defined in vendor-specific applications MUST include either one Result-Code AVP or one Experimental-Result AVP. the missing vendor id. Experimental-Result-Code AVP
The Experimental-Result-Code AVP (AVP Code 298) is of type Unsigned32 and contains a vendor-assigned value representing the result of processing the request. 7. If the failure reason is omission of a required AVP. and a zero filled payload of the minimum required length for the omitted AVP will be added. Its Data field has the following ABNF grammar: AVP Format Experimental-Result ::= < AVP Header: 297 > { Vendor-Id } { Experimental-Result-Code } The Vendor-Id AVP (see Section 5. an AVP with the missing AVP code.7.
Calhoun. The first involves authentication and authorization.3.3) in this grouped AVP identifies the vendor responsible for the assignment of the result code which follows. and indicates whether a particular vendor-specific request was completed successfully or whether an error occurred. Diameter User Sessions Diameter can provide two different types of services to applications. It is recommended that vendor-specific result codes follow the same conventions given for the Result-Code AVP regarding the different types of result codes and the handling of errors (for non 2xxx values). et al. Experimental-Result AVP
The Experimental-Result AVP (AVP Code 297) is of type Grouped.RFC 3588
Diameter Based Protocol
September 2003
A Diameter message MAY contain one Failed-AVP AVP. AVP Format <Failed-AVP> ::= < AVP Header: 279 > 1* {AVP} 7. 8. containing the entire AVP that could not be processed successfully.
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.

Of course.. and a user requests access to the network.. When a Diameter server authorizes a user to use network resources for a finite amount of time. Services provided past the expiration of the Authorization-Lifetime and Auth-Grace-Period AVPs are the responsibility of the access device. An access device that does not expect to send a re-authorization or a session termination request to the server MAY include the AuthSession-State AVP with the value set to NO_STATE_MAINTAINED as a hint to the server. it agrees that since no session termination message will be received once service to the user is terminated.
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.
Calhoun. NASREQ). combined with the Auth-Grace-Period AVP.RFC 3588
Diameter Based Protocol
September 2003
When a service makes use of the authentication and/or authorization portion of an application. The auth request is defined in a service specific Diameter application (e.g. and it is willing to extend the authorization via a future request. it MUST add the AuthorizationLifetime AVP to the answer message. accounting. The request contains a Session-Id AVP. If the answer message from the server contains a different value in the Auth-Session-State AVP (or the default value if the AVP is absent). The Auth-Grace-Period AVP contains the number of seconds following the expiration of the Authorization-Lifetime. the actual cost of services rendered is clearly outside the scope of the protocol. the access device MUST follow the server’s directives. the Diameter client issues an auth request to its local server.g. subsequent authorization. The base protocol does not include any authorization request messages. Note that if payment for services is expected by the serving realm from the user’s home realm. Note that the value NO_STATE_MAINTAINED MUST NOT be set in subsequent reauthorization requests and answers. the base protocol does define a set of messages that is used to terminate user sessions. These are used to allow servers that maintain state information to free resources. et al. However. If the server accepts the hint. it cannot maintain state for the session. after which the server will release all state information related to the user’s session. The Authorization-Lifetime AVP defines the maximum number of seconds a user MAY make use of the resources before another authorization request is expected by the server. implies the maximum length of the session the home realm is willing to be fiscally responsible for. since these are largely application-specific and are defined in a Diameter application document. which is used in subsequent messages (e. the Authorization-Lifetime AVP. The Session-Id AVP is a means for the client and servers to correlate a Diameter message with a user session. etc) relating to the user’s session.

and which MUST be observed by all Diameter implementations that make use of the authentication and/or authorization portion of a Diameter application.
Calhoun. The second two state machines are used when the server does not maintain session state. Here again. This could be due to the peer being down. the event ’Failure to send X’ means that the Diameter agent is unable to send command X to the desired destination.1. In the state table. et al.. The event ’X successfully sent’ is the complement of ’Failure to send X’.RFC 3588
Diameter Based Protocol
September 2003
When a service only makes use of the Accounting portion of the Diameter protocol. The first two describe a session in which the server is maintaining session state.g. the session termination messages are not used. or due to the peer sending back a transient failure or temporary protocol error notification DIAMETER_TOO_BUSY or DIAMETER_LOOP_DETECTED in the Result-Code AVP of the corresponding Answer command. any resources that were allocated for the particular session must be released. the other from a server perspective. representing the life cycle of Diameter sessions. if applicable. Mobile IPv4. There are four different authorization session state machines supported in the Diameter base protocol. NASREQ). indicated by the value of the Auth-Session-State AVP (or its absence). even in combination with an application. the Session-Id is still used to identify user sessions. Authorization Session State Machine
This section contains a set of finite state machines. the other from a server perspective. Any event not listed in the state machines MUST be considered as an error condition.
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. MUST be returned to the originator of the message. since a session is signaled as being terminated by issuing an accounting stop message. and an answer. One describes the session from a client perspective. When a session is moved to the Idle state. However. one describes the session from a client perspective. The term Service-Specific below refers to a message defined in a Diameter application (e. 8.

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. STATEFUL State Event Action New State ------------------------------------------------------------Idle Service-specific authorization Send Open request received. Send STR. user is not authorized specific answer Service-specific authorization Send Open request received. client will comply with request to end the session
Send ASA Discon with Result-Code = SUCCESS. is not authorized specific answer. specific answer Service-specific authorization Send Idle request received. Send ASA Open with Result-Code != SUCCESS Send STR Discon
Open
ASR Received. and failed serv. and user failed serv. et al. Idle user/device
The following state machine is observed by a server when it is maintaining state for the session: SERVER. specific answer Idle Service-specific authorization Send Idle request received. client will not comply with request to end the session
Open
Authorization-Lifetime + Auth-Grace-Period expires on access device ASR Received STA Received
Discon Discon
Send ASA
Discon
Discon. and user successful is authorized serv. and successful user is authorized serv. Cleanup Home server wants to terminate the service Send ASR Discon
Open
Open
Open
Calhoun.RFC 3588
Diameter Based Protocol
September 2003
Open
ASR Received.

STATELESS State Event Action New State ------------------------------------------------------------Idle Client or Device Requests Send Pending access service specific auth req Pending Successful Service-specific authorization answer received with Auth-SessionState set to NO_STATE_MAINTAINED Failed Service-specific authorization answer received Session-Timeout Expires on Access Device Service to user is terminated Grant Access Open
Pending
Cleanup
Idle
Open
Discon. et al.
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. Session-Timeout expires on home server Failure to send ASR
Cleanup
Idle
Open
Cleanup
Idle
Discon
Wait.
Idle
The following state machine is observed by a client when state is not maintained on the server: CLIENT.RFC 3588
Diameter Based Protocol
September 2003
Open
Authorization-Lifetime (and Auth-Grace-Period) expires on home server. Idle user/device Discon. Idle user/device
Open
Calhoun. Discon resend ASR Cleanup Idle
Discon
ASR successfully sent and ASA Received with Result-Code ASA Received
Not Discon Any
None
No Change. Cleanup.
STR Received
Send STA.

fraud detection. Applications MAY define requirements on when to accept accounting records based on the used value of Accounting-Realtime-Required AVP. Implementations of Diameter MAY perform checking. However. Idle request received. This is the second state machine in this section described below. and specific successfully processed answer 8.2. et al.8 for Accounting AVPs. credit limits checks. the use of this state machine is recommended only in applications where the value of the Accounting-Realtime-Required AVP is DELIVER_AND_GRANT. The server side in the accounting state machine depends in some cases on the particular application. they are not standardized by the Diameter specifications. The first state machine is to be observed by clients. Both base Diameter AVPs as well as application specific AVPs MAY be inspected as a part of these tasks. STATELESS State Event Action New State ------------------------------------------------------------Idle Service-specific authorization Send serv. and hence accounting connectivity problems are required to cause the serviced user to be disconnected. Note that such tracking is incompatible with the ability to sustain long duration connectivity problems. correlation.RFC 3588
Diameter Based Protocol
September 2003
The following state machine is observed by a server when it is not maintaining state for the session: SERVER. The Diameter base protocol defines a default state machine that MUST be followed by all applications that have not specified other state machines. The default server side state machine requires the reception of accounting records in any order and at any time. Otherwise. as these tasks are typically application or even policy dependent. and other tasks based on these records.7 for Accounting Command Codes and Section 9. the Diameter base protocol defines one optional server side state machine that MAY be followed by applications that require keeping track of the session state at the accounting server. The tasks can happen either immediately after record reception or in a post-processing phase. and so on. Accounting Session State Machine
The following state machines MUST be supported for applications that have an accounting portion or that require only accounting services. ordering. and does not place any standards requirement on the processing of these records. See Section 9. Therefore.
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. records produced by the client
Calhoun. However.

e. the event ’Failure to send’ means that the Diameter client is unable to communicate with the desired destination. et al. if the given application has both authentication/authorization and accounting portions. MUST be returned to the originator of the message.
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.g. Ts MAY be set to two times the value of the Acct_Interim_Interval so as to avoid the accounting session in the Diameter server to change to Idle state in case of short transient network failure. Event or buffered record. cause the STR message to be sent. and a corresponding answer. The state machine is supervised by a supervision session timer Ts. Any event not listed in the state machines MUST be considered as an error condition. Idle Client or device requests a one-time service Send PendingE accounting event req Send record PendingB
Idle
Records in storage
Calhoun. Interim. PendingE and PendingB stand for pending states to wait for an answer to an accounting request related to a Start. or DIAMETER_LOOP_DETECTED in the Result-Code AVP of the Accounting Answer command. respectively. which the value should be reasonably higher than the Acct_Interim_Interval value. PendingI. Stop. This state machine is the third state machine in this section. CLIENT. or due to the peer sending back a transient failure or temporary protocol error notification DIAMETER_OUT_OF_SPACE.. This could be due to the peer being down. DIAMETER_TOO_BUSY. Note that the action ’Disconnect user/dev’ MUST have an effect also to the authorization session state table. In the state table. The event ’Failed answer’ means that the Diameter client received a non-transient failure notification in the Accounting Answer command.RFC 3588
Diameter Based Protocol
September 2003
may be lost by the server which no longer accepts them after the connectivity is re-established. ACCOUNTING State Event Action New State ------------------------------------------------------------Idle Client or device requests Send PendingS access accounting start req. if applicable. The states PendingS. PendingL.

RFC 3588
Diameter Based Protocol
September 2003
PendingS
Successful accounting start answer received Failure to send and buffer Store space available and realtime Start not equal to DELIVER_AND_GRANT Record Failure to send and no buffer space available and realtime equal to GRANT_AND_LOSE Failure to send and no buffer space available and realtime not equal to GRANT_AND_LOSE Failed accounting start answer received and realtime equal to GRANT_AND_LOSE
Open
PendingS
Open
PendingS
Open
PendingS
Disconnect Idle user/dev
PendingS
Open
PendingS
Failed accounting start answer Disconnect Idle received and realtime not user/dev equal to GRANT_AND_LOSE User service terminated Store stop record PendingS
PendingS
Open
Interim interval elapses
Open
User service terminated
Send PendingI accounting interim record Send PendingL accounting stop req. et al.
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. Open
PendingI
Successful accounting interim answer received Failure to send and (buffer space available or old record can be overwritten) and realtime not equal to DELIVER_AND_GRANT Failure to send and no buffer space available and realtime equal to GRANT_AND_LOSE Store interim record
PendingI
Open
PendingI
Open
Calhoun.

Restart Ts Send Idle accounting stop answer. Result-Code = OUT_OF_ SPACE Send Open accounting interim answer. if the service supports this particular feature.
Open
Accounting stop request received. for pre-paid services. An access device that receives a RAR message with Session-Id equal to a currently active session MUST initiate a re-auth towards the user. no space left to store records
Send Idle accounting answer.
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. For example. Each Diameter application MUST state whether service-initiated re-auth is supported.
Server-Initiated Re-Auth
A Diameter server may initiate a re-authentication and/or reauthorization service for a particular session by issuing a Re-AuthRequest (RAR). et al.
Calhoun. since some applications do not allow access devices to prompt the user for re-auth. Stop Ts Send Idle accounting answer. the Diameter server that originally authorized a session may need some confirmation that the user is still using the services.3. no space left to store records
Open
Session supervision timer Ts expired
8. Stop Ts Stop Ts Idle
Open
Interim record received. and successfully processed
Open
Accounting request received.RFC 3588
Diameter Based Protocol
September 2003
Idle
Accounting request received. and successfully processed. Result-Code = OUT_OF_ SPACE.

PXY > Session-Id > Result-Code } Origin-Host } Origin-Realm } User-Name ] Origin-State-Id ] Error-Message ] Error-Reporting-Host ] Failed-AVP ] Redirect-Host ] Redirect-Host-Usage ] Redirect-Host-Cache-Time ] Proxy-Info ] AVP ]
8. a proxy may modify an authorization answer. etc. the access device that provided the service MUST issue a SessionTermination-Request (STR) message to the Diameter server that authorized the service. both for tracking purposes as well as to allow stateful agents to release any resources that they may have provided for the user’s session. prior to forwarding the message to the access device. or because the access device does not support a mandatory AVP returned in the authorization. This could occur.4.
Session Termination
It is necessary for a Diameter server that authorized a session. or because the access device is unwilling to provide the type of service requested in the authorization. An STR MUST be issued when a user session terminates for any reason. including user logoff. The access device also MUST issue an STR for a session that was authorized but never actually started. For sessions whose state is not being maintained. It is also possible that a session that was authorized is never actually started due to action of a proxy. administrative action. For example. to be notified when that session is no longer active. If the answer did not contain an Auth-Session-State AVP with the value
Calhoun. due to a sudden resource shortage in the access device.
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. orderly shutdown of the access device. expiration of Session-Timeout. termination upon receipt of an Abort-SessionRequest (see below). When a user session that required Diameter authorization terminates. etc. for example. this section is not used. to notify it that the session is no longer active.RFC 3588
Diameter Based Protocol
September 2003
Message Format <RAA> ::= < < { { { [ [ [ [ * [ * [ [ [ * [ * [ Diameter Header: 258. et al. converting the result from success to failure. for which it is maintaining state.

et al. indicated by the Command-Code set to 275 and the Command Flags’ ’R’ bit set. thus.g. is sent by the access device to inform the Diameter Server that an authenticated and/or authorized session is being terminated. The access device is not expected to provide service beyond the expiration of these timers.RFC 3588
Diameter Based Protocol
September 2003
NO_STATE_MAINTAINED.. A Diameter server also MUST clean up resources when the SessionTimeout expires. or when the Authorization-Lifetime and the AuthGrace-Period AVPs expires without receipt of a re-authorization request. Session-Termination-Request
The Session-Termination-Request (STR).
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. session state) associated with the Session-Id specified in the STR. A Diameter server that receives an STR message MUST clean up resources (e.4. a proxy that causes an authorized session not to be started MUST issue an STR to the Diameter server that authorized the session. and return a Session-Termination-Answer. PXY > Session-Id > Origin-Host } Origin-Realm } Destination-Realm } Auth-Application-Id } Termination-Cause } User-Name ] Destination-Host ] Class ] Origin-State-Id ] Proxy-Info ] Route-Record ] AVP ]
Calhoun. expiration of either of these timers implies that the access device may have unexpectedly shut down.1. regardless of whether an STR for that session is received. REQ. since the access device has no way of knowing that the session had been authorized. Message Format <STR> ::= < < { { { { { [ [ * [ [ * [ * [ * [ Diameter Header: 275. 8.

Any intermediate server in the Proxy-Chain MAY also release any resources. PXY > Session-Id > Result-Code } Origin-Host } Origin-Realm } User-Name ] Class ] Error-Message ] Error-Reporting-Host ] Failed-AVP ] Origin-State-Id ] Redirect-Host ] Redirect-Host-Usage ] ^ [ Redirect-Max-Cache-Time ] * [ Proxy-Info ] * [ AVP ]
8.
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. et al. An access device that receives an ASR with Session-ID equal to a currently active session MAY stop the session.
Aborting a Session
A Diameter server may request that the access device stop providing service for a particular session by issuing an Abort-Session-Request (ASR). indicated by the Command-Code set to 275 and the message flags’ ’R’ bit clear.2. is sent by the Diameter Server to acknowledge the notification that the session has been terminated.RFC 3588
Diameter Based Protocol
September 2003
8. For example.4. On the other hand. an operator may maintain a management server for the purpose of issuing ASRs to administratively remove users from the network. the Diameter Server MUST release all resources for the session indicated by the Session-Id AVP. and MAY contain an indication that an error occurred while servicing the STR. Whether the access
Calhoun.
Session-Termination-Answer
The Session-Termination-Answer (STA). if necessary. Message Format <STA> ::= < < { { { [ * [ [ [ * [ [ * [ [ Diameter Header: 275. Upon sending or receipt of the STA. the Diameter server that originally authorized the session may be required to cause that session to be stopped for credit or other reasons that were not anticipated when the session was first authorized.5. The Result-Code AVP MUST be present.

Abort-Session-Answer
The Abort-Session-Answer (ASA). Result-Code is set to DIAMETER_UNKNOWN_SESSION_ID. Note that if the access device does stop the session upon receipt of an ASR.and/or configuration-dependent.RFC 3588
Diameter Based Protocol
September 2003
device stops the session or not is implementation. it issues an STR to the authorizing server (which may or may not be the agent issuing the ASR) just as it would if the session were terminated for any other reason. indicated by the Command-Code set to and the message flags’ ’R’ bit set. If the access device does not stop the session for any other reason. to request that session identified by the Session-Id be stopped.5. is sent in response to the ASR. The 274 the the Abort-Session-Request Abort-Session-Request (ASR). indicated by the Command-Code set to 274 and the message flags’ ’R’ bit clear. the access device MUST respond with an Abort-Session-Answer. an access device may honor ASRs from certain agents only.
Message Format <ASR> ::= < < { { { { { [ [ * [ * [ * [ Diameter Header: 274.5. If the session identified by Session-Id in the ASR was successfully terminated. 8. including a Result-Code AVP to indicate what action it took. The Result-Code AVP MUST be present. et al.2. In any case. REQ. PXY > Session-Id > Origin-Host } Origin-Realm } Destination-Realm } Destination-Host } Auth-Application-Id } User-Name ] Origin-State-Id ] Proxy-Info ] Route-Record ] AVP ]
8.
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.1. Result-Code is set to DIAMETER_SUCCESS. If the session is not currently active. and indicates the disposition of the request.
Calhoun. may be sent by any server to access device that is providing session service. For example. Result-Code is set to DIAMETER_UNABLE_TO_COMPLY.

due to unanticipated shutdown of an access device. By including Origin-State-Id in request messages. and MAY also issues STRs for all such lost sessions that were authorized on upstream servers. By including Origin-State-Id in CER/CEA messages.
Calhoun. PXY > Session-Id > Result-Code } Origin-Host } Origin-Realm } User-Name ] Origin-State-Id ] Error-Message ] Error-Reporting-Host ] Failed-AVP ] Redirect-Host ] Redirect-Host-Usage ] Redirect-Max-Cache-Time ] Proxy-Info ] AVP ]
8. it may assume that the issuer has lost state since the previous message and that all sessions that were active under the lower Origin-StateId have been terminated. However. use of this mechanism across proxies is opportunistic rather than reliable. to allow session state to be cleaned up globally. The Diameter server MAY clean up all session state associated with such lost sessions. an access device allows a next-hop server to determine immediately upon connection whether the device has lost its sessions since the last connection. an access device also allows a server with which it communicates via proxy to make such a determination. Thus.
Inferring Session Termination from Origin-State-Id
Origin-State-Id is used to allow rapid detection of terminated sessions for which no STR would have been issued. a server that is not directly connected with the access device will not discover that the access device has been restarted unless and until it receives a new request from the access device. but useful nonetheless. When a Diameter server receives an Origin-State-Id that is greater than the Origin-State-Id previously received from the same issuer. et al.6.RFC 3588
Diameter Based Protocol
September 2003
Message Format <ASA> ::= < < { { { [ [ [ [ * [ * [ [ [ * [ * [ Diameter Header: 274.
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.

Note any value other than both MAY cause RADIUS interoperability issues. and MAY be any sequence that the client can guarantee to be eternally unique. however." character.
Auth-Request-Type AVP
The Auth-Request-Type AVP (AVP Code 274) is of type Enumerated and is included in application-specific auth requests to inform the peers whether a user is to be authenticated only. AUTHORIZE_ONLY 2 The request being sent is for authorization only. and MUST contain the relevant application specific authentication AVPs that are needed by the Diameter server to authenticate the user. and MUST contain the application specific authorization AVPs that are necessary to identify the service being requested/offered. All messages pertaining to a specific session MUST include only one Session-Id AVP and the same value MUST be used throughout the life of a session. (square brackets [] indicate an optional element):
Calhoun. the following format is recommended. authorized only or both. The request MUST include both the relevant application specific authentication information. When present. a recommended format for the implementation-defined portion is outlined below.RFC 3588
Diameter Based Protocol
September 2003
8.8. The remainder of the Session-Id is delimited by a ". 8. The Session-Id MUST begin with the sender’s identity encoded in the DiameterIdentity type (see Section 4. AUTHORIZE_AUTHENTICATE 3 The request contains a request for both authentication and authorization. Session-Id AVP
The Session-Id AVP (AVP Code 263) is of type UTF8String and is used to identify a specific session (see Section 8). and may be needed to correlate historical authentication information with accounting information. The following values are defined: AUTHENTICATE_ONLY 1 The request being sent is for authentication only.7. as it is meant to uniquely identify a user session without reference to any other information.4). and authorization information necessary to identify the service being requested/offered. The Session-Id MUST be globally and eternally unique. the Session-Id SHOULD appear immediately following the Diameter Header (see Section 3). et al.
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. The Session-Id includes a mandatory portion and an implementation-defined portion.

523. 8. and the low 32 bits MAY be initialized to zero.<high 32 bits>.acme. et al. <optional value> is implementation specific but may include a modem’s device Id. an implementation MAY keep track of the increasing value in non-volatile memory. value could create significant Diameter traffic. which in most cases is done by the client. timestamp. assuming the reboot process takes longer than a second.88 The Session-Id is created by the Diameter application initiating the session.1.1876543210. in which there is no optional value: accesspoint7.RFC 3588
Diameter Based Protocol
September 2003
<DiameterIdentity>. If both this AVP and the Session-Timeout AVP are present in a message. Great care should be taken when the AuthorizationLifetime value is determined. and a successful auth response with this AVP set to zero is used to signal that the next authentication method is to be immediately initiated. This is typically used in cases where multiple authentication methods are used. Authorization-Lifetime AVP
The Authorization-Lifetime AVP (AVP Code 291) is of type Unsigned32 and contains the maximum number of seconds of service to be provided to the user before the user is to be re-authenticated and/or reauthorized.mobile@200.acme.<optional value>] <high 32 bits> and <low 32 bits> are decimal representations of the high and low 32 bits of a monotonically increasing 64-bit value.523 Example.<low 32 bits>[. The absence of this AVP. which could congest both the network and the agents. non-zero. etc. Note that a Session-Id MAY be used for both the authorization and accounting commands of a given application. since a low.com. the high 32 bits of the 64-bit value MAY be initialized to the time.
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. Alternatively. a layer 2 address. the value of the latter MUST NOT be smaller than the Authorization-Lifetime AVP.9. A value of zero (0) means that immediate re-auth is necessary by the access device. Example. The 64-bit value is rendered in two part to simplify formatting by 32-bit processors.com.1. At startup. This will for practical purposes eliminate the possibility of overlapping Session-Ids after a reboot.
Calhoun. or a value of all ones (meaning all bits in the 32 bit field are set to one) means no re-auth is expected.1876543210. in which there is an optional value: accesspoint7.

but the value in the server’s answer message is binding. The following values are defined:
Calhoun. This AVP MAY be provided by the client as a hint of the maximum lifetime that it is willing to accept. and the access device MUST issue a session termination message when service to the user is terminated. Auth-Session-State AVP
The Auth-Session-State AVP (AVP Code 277) is of type Enumerated and specifies whether state is maintained for a particular session.
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. If the answer message contains an Authorization-Lifetime AVP with a positive value. the Re-Auth-Request-Type AVP MUST be present in an answer message.10.12. 8. or smaller. The following values are supported: STATE_MAINTAINED 0 This value is used to specify that session state is being maintained. Auth-Grace-Period AVP
The Auth-Grace-Period AVP (AVP Code 276) is of type Unsigned32 and contains the number of seconds the Diameter server will wait following the expiration of the Authorization-Lifetime AVP before cleaning up resources for the session. This is the default value. NO_STATE_MAINTAINED 1 This value is used to specify that no session termination messages will be sent by the access device upon expiration of the Authorization-Lifetime.RFC 3588
Diameter Based Protocol
September 2003
An Authorization-Lifetime AVP MAY be present in re-authorization messages. 8. and contains the number of seconds the user is authorized to receive service from the time the re-auth answer message is received by the access device. However. et al. than the one provided by the client. The client MAY include this AVP in requests as a hint to the server. the server MAY return a value that is equal to. Re-Auth-Request-Type AVP
The Re-Auth-Request-Type AVP (AVP Code 285) is of type Enumerated and is included in application-specific auth answers to inform the client of the action expected upon expiration of the Authorization-Lifetime. 8.11.

9). This AVP MAY be provided by the client as a hint of the maximum timeout that it is willing to accept. Session-Timeout AVP
The Session-Timeout AVP (AVP Code 27) [RADIUS] is of type Unsigned32 and contains the maximum number of seconds of service to be provided to the user before termination of the session. User-Name AVP
The User-Name AVP (AVP Code 1) [RADIUS] is of type UTF8String.13. A value of zero. 8. A Session-Timeout AVP MAY be present in a re-authorization answer message. This is the default value if the AVP is not present in answer messages that include the AuthorizationLifetime. A session that terminates on an access device due to the expiration of the Session-Timeout MUST cause an STR to be issued. and is used to indicate the reason why a session was terminated on the access device. in a format consistent with the NAI specification [NAI].
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.14.RFC 3588
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September 2003
AUTHORIZE_ONLY 0 An authorization only re-auth is expected upon expiration of the Authorization-Lifetime. et al. or the absence of this AVP. The following values are defined:
Calhoun. unless both the access device and the home server had previously agreed that no session termination messages would be sent (see Section 8. means that this session has an unlimited number of seconds before termination. 8. than the one provided by the client. the server MAY return a value that is equal to.15. When both the Session-Timeout and the Authorization-Lifetime AVPs are present in an answer message. Termination-Cause AVP
The Termination-Cause AVP (AVP Code 295) is of type Enumerated. 8. which contains the User-Name. and contains the remaining number of seconds from the beginning of the re-auth. the former MUST be equal to or greater than the value of the latter. However. AUTHORIZE_AUTHENTICATE 1 An authentication and authorization re-auth is expected upon expiration of the Authorization-Lifetime. or smaller.

and service has been terminated. it MUST either remove Origin-State-Id or modify it appropriately as well. DIAMETER_BAD_ANSWER 3 This value indicates that the authorization answer received by the access device was not processed successfully. if present.
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. 8. DIAMETER_AUTH_EXPIRED 6 The user’s access was terminated since its authorized session time has expired. If a proxy modifies Origin-Host.RFC 3588
Diameter Based Protocol
September 2003
DIAMETER_LOGOUT 1 The user initiated a disconnect DIAMETER_SERVICE_NOT_PROVIDED 2 This value is used when the user disconnected prior to the receipt of the authorization answer message. is a monotonically increasing value that is advanced whenever a Diameter entity restarts with loss of previous state. DIAMETER_SESSION_TIMEOUT 8 The user’s session has timed out. for example upon reboot. due to administrative reasons. Origin-State-Id MAY be included in any Diameter message. Origin-State-Id AVP
The Origin-State-Id AVP (AVP Code 278).
The Origin-State-Id. et al. of type Unsigned32. DIAMETER_USER_MOVED 7 The user is receiving services from another access device.16. DIAMETER_ADMINISTRATIVE 4 The user was not granted access. such as the receipt of a Abort-SessionRequest message. or was disconnected. A Diameter entity issuing this AVP MUST this AVP each time its state is reset.
Calhoun. MUST reflect the state of the entity indicated by Origin-Host. DIAMETER_LINK_BROKEN 5 The communication to the user was abruptly disconnected. counter retained in non-volatile memory create a higher value for A Diameter entity MAY set or it MAY use an incrementing across restarts. Origin-State-Id to the time of startup. including CER.

18. future re-auth messages for this session MUST NOT include the Destination-Host AVP. If present. if known. the default value. the STR message for this session MUST NOT include the Destination-Host AVP. that is. all accounting messages for this session MUST NOT include the Destination-Host AVP. it MUST either not include Origin-State-Id in any message. the default value.
ACCOUNTING 4 When set. MUST be present in all accounting messages for this session. Session-Binding AVP
The Session-Binding AVP (AVP Code 270) is of type Unsigned32. If an access device does not intend for such inferences to be made. et al. the default value. This field is a bit mask. the Destination-Host AVP. If present. this AVP MAY inform the Diameter client that if a
Calhoun. and MAY be present in application-specific authorization answer messages that either do not include the Session-Binding AVP or include the Session-Binding AVP with any of the bits set to a zero value. When cleared. By including Origin-State-Id in a message. and MAY be present in application-specific authorization answer messages. and the following bits have been defined: RE_AUTH 1 When set. STR 2 When set. the Destination-Host AVP MUST be present in the STR message for this session. 8. or set its value to 0. When cleared.17. this AVP MAY inform the Diameter client that all future application-specific re-auth messages for this session MUST be sent to the same authorization server. any session active prior to restart will have been lost. This AVP MAY also specify that a Session-Termination-Request message for this session MUST be sent to the same authorizing server.RFC 3588
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September 2003
Typically. 8.
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. When cleared. it allows other Diameter entities to infer that sessions associated with a lower Origin-State-Id are no longer active. the Destination-Host AVP MUST be present in all re-auth messages for this session. Origin-State-Id is used by an access device that always starts up with no active sessions. Session-Server-Failover AVP
The Session-Server-Failover AVP (AVP Code 271) is of type Enumerated.

and SHOULD be present in application-specific authorization answer messages whose Result-Code AVP is set to DIAMETER_MULTI_ROUND_AUTH. If the second delivery fails for re-auth.19. 8. If STR message delivery fails. et al. resend the failed message without the Destination-Host AVP present. assume that re-authorization succeeded. Class AVPs found in a re-authorization answer message override the ones found in any previous authorization answer message. When one or more Class AVPs are present in application-specific authorization answer messages. session termination and accounting messages. resend the failed message without the Destination-Host AVP present. When absent. TRY_AGAIN 1 If either the re-auth or the STR message delivery fails. Multi-Round-Time-Out AVP
The Multi-Round-Time-Out AVP (AVP Code 272) is of type Unsigned32. and do not attempt any subsequent attempts. the default value is REFUSE_SERVICE. Diameter server implementations SHOULD NOT return Class AVPs that require more than 4096 bytes of storage on the Diameter client. the Diameter client SHOULD issue a subsequent message without the Destination-Host AVP. If the second delivery fails for STR.20. ALLOW_SERVICE 2 If re-auth message delivery fails. they MUST be present in subsequent re-authorization. terminate the session. terminate the session. Class AVP
The Class AVP (AVP Code 25) is of type OctetString and is used to by Diameter servers to return state information to the access device. terminate service with the user.
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. The following values are supported: REFUSE_SERVICE 0 If either the re-auth or the STR message delivery fails. 8. TRY_AGAIN_ALLOW_SERVICE 3 If either the re-auth or the STR message delivery fails.RFC 3588
Diameter Based Protocol
September 2003
re-auth or STR message fails due to a delivery problem. This AVP contains the maximum number of seconds that the access device MUST provide the user in responding to an authentication request. assume re-authorization succeeded. A Diameter client that receives Class AVPs whose size exceeds local available storage MUST terminate the session.
Calhoun.

such as the need to perform credit limit checks and fraud detection. et al.RFC 3588
Diameter Based Protocol
September 2003
8. This may be sufficient for many applications. 1900 00:00 UTC. or it could be handled using another protocol.1.
Calhoun. transport protocols used under Diameter typically batch several requests in the same packet under heavy traffic conditions. The server (or agents) uses the Acct-Interim-Interval and Accounting-Realtime-Required AVPs to control the operation of the Diameter peer operating as a client. Should batched accounting be required in the future. Note that batch accounting is not a requirement. The authorization server (chain) directs the selection of proper transfer strategy. when present. Accounting This accounting protocol is based on a server directed model with capabilities for real-time delivery of accounting information. Several fault resilience methods [ACCMGMT] have been built in to the protocol in order minimize loss of accounting data in various fault situations and under different assumptions about the capabilities of the used devices. This information includes accounting record timeliness requirements. however. The Acct-Interim-Interval AVP.
Event-Timestamp AVP
The Event-Timestamp (AVP Code 55) is of type Time. instructs the Diameter node acting as a client to produce accounting records continuously even during a session. based on its knowledge of the user and relationships of roaming partnerships. 9.21. Accounting-Realtime-Required AVP is used to control the behavior of the client when the transfer of accounting records from the Diameter client is delayed or unsuccessful. real-time transfer of accounting records is a requirement. As discussed in [ACCMGMT]. in seconds since January 1. and MAY be included in an Accounting-Request and Accounting-Answer messages to record the time that the reported event occurred. that even if at the Diameter layer accounting requests are processed one by one.
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. and is therefore not supported by Diameter. a new Diameter application will need to be created. Note. 9. Server Directed Model
The server directed model means that the device generating the accounting data gets information from either the authorization server (if contacted) or the accounting server regarding the way accounting data shall be forwarded.

MobileIP). 9. Each Diameter Accounting protocol message MAY be compressed. Protocol Messages
A Diameter node that receives a successful authentication and/or authorization messages from the Home AAA server MUST collect accounting information for the session. The Accounting-Answer message includes the Result-Code AVP. Diameter peers acting as clients MUST implement the use of failover to guard against server failures and certain network failures. the latest value received SHOULD be used in further accounting activities for the same session. If IPsec and IKE are used to secure the Diameter session. A rejected Accounting-Request message MAY cause the user’s session to be terminated.g. which MUST reply with the Accounting-Answer message to confirm reception. The Accounting-Request message is used to transmit the accounting information to the Home AAA server. 9. The application MUST assume that the AVPs described in this document will be present in all Accounting messages.4. in order to reduce network bandwidth usage. which MAY indicate that an error was present in the accounting message. NASREQ. When one of these AVPs is present. 9. Application document requirements
Each Diameter application (e.2. depending on the value of the Accounting-Realtime-Required AVP received earlier for the session in question. et al. Diameter peers acting as agents or related off-line processing systems MUST detect duplicate accounting records caused by the sending of same record to several servers and duplication of messages
Calhoun. MUST define their Service-Specific AVPs that MUST be present in the Accounting-Request message in a section entitled "Accounting AVPs". If TLS is used to secure the Diameter session.
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. so only their respective service-specific AVPs need to be defined in this section. Fault Resilience
Diameter Base protocol mechanisms are used to overcome small message loss and network faults of temporary nature.RFC 3588
Diameter Based Protocol
September 2003
The Diameter accounting server MAY override the interim interval or the realtime requirements by including the Acct-Interim-Interval or Accounting-Realtime-Required AVP in the Accounting-Answer message.. then TLS compression [TLS] MAY be used. then IP compression [IPComp] MAY be used and IKE [IKE] MAY be used to negotiate the compression parameters.3.

It is an implementation dependent matter for the client to accept new sessions under this condition. If the authorization server has not directed interim accounting to be enabled for the session. 9. two accounting records MUST be generated for each service of type session. meaning that the start and stop of the event are simultaneous. If the accounted service is a one-time event. Appendix C discusses duplicate detection needs and implementation issues.RFC 3588
Diameter Based Protocol
September 2003
in transit. The client MAY remove oldest. Upon a reboot. The client SHOULD NOT remove the accounting data from any of its memory areas before the correct Accounting-Answer has been received. and server failures. and possibly. then the AVP MUST use the values START_RECORD. et al. and other relevant information in the records. If the accounted service is of a measurable length. network partitions. end-toend security may be used for authentication purposes. the Session-Id AVP MUST be present. INTERIM_RECORD. the client SHOULD store new accounting records there as soon as the records are created and until a positive acknowledgement of their reception from the Diameter Server has been received. When the initial
Calhoun. A further application of this protocol may include AVPs to control how many accounting records may at most be stored in the Diameter client without committing them to the non-volatile memory or transferring them to the Diameter server. If strong authentication across agents is required. undelivered or yet unacknowledged accounting data if it runs out of resources such as memory. STOP_RECORD. This detection MUST be based on the inspection of the Session-Id and Accounting-Record-Number AVP pairs. Different types of accounting records are sent depending on the actual type of accounted service and the authorization server’s directions for interim accounting.5. session length. the User-Name AVP MUST be present if it is available to the Diameter client. the client MUST starting sending the records in the non-volatile memory to the accounting server with appropriate modifications in termination cause. then the Accounting-Record-Type AVP MUST be present and set to the value EVENT_RECORD.
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. Diameter clients MAY have non-volatile memory for the safe storage of accounting records over reboots or extended network failures. If such memory is available. Accounting Records
In all accounting records.

marked INTERIM_RECORD. each with their own unique Session-Id. A particular Diameter application specification MUST define the type of sequences that MUST be used. In such cases. correlation is performed using the Session-Id. if a new record is being generated for the same session. The one sequence that is sent MUST be either one record with Accounting-Record-Type AVP set to the value EVENT_RECORD. However.
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. which is globally unique (see Section 8.. a server that
Calhoun. Such applications would send messages with a constant Session-Id AVP. but a different Accounting-Sub-Session-Id AVP. Specific applications MAY require different a Session-ID for accounting messages. the value MUST be STOP_RECORD. is used during the authorization phase to identify a particular session. or several records starting with one having the value START_RECORD. When the last Accounting-Request is sent. the Acct-Multi-SessionId AVP is used for correlation.g.6. Accounting messages MAY use a different Session-Id from that sent in authorization messages. The Diameter client MUST overwrite any previous interim accounting records that are locally stored for delivery.RFC 3588
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September 2003
Accounting-Request for a given session is sent. there are certain applications that require multiple accounting sub-sessions. Furthermore. In these cases. the Diameter client MUST produce additional records between the START_RECORD and STOP_RECORD. This ensures that only one pending interim record can exist on an access device for any given session.8). During authorization. Mobile IPv4). et al. It is important to note that receiving a STOP_RECORD with no Accounting-Sub-Session-Id AVP when sub-sessions were originally used in the START_RECORD messages implies that all sub-sessions are terminated. A particular value of Accounting-Sub-Session-Id MUST appear only in one sequence of accounting records from a DIAMETER client. followed by zero or more INTERIM_RECORD and a single STOP_RECORD. Correlation of Accounting Records
The Diameter protocol’s Session-Id AVP. there are certain applications where a user receives service from different access devices (e. The production of these records is directed by Acct-Interim-Interval as well as any re-authentication or re-authorization of the session. 9. except for the purposes of retransmission. the AccountingRecord-Type AVP MUST be set to the value START_RECORD. Services that do not require any authorization still use the Session-Id AVP to identify sessions. If the authorization server has directed interim accounting to be enabled.

RFC 3588

Diameter Based Protocol

September 2003

determines that a request is for an existing session SHOULD include the Acct-Multi-Session-Id AVP, which the access device MUST include in all subsequent accounting messages. The Acct-Multi-Session-Id AVP MAY include the value of the original Session-Id. It’s contents are implementation specific, but MUST be globally unique across other Acct-Multi-Session-Id, and MUST NOT change during the life of a session. A Diameter application document MUST define the exact concept of a session that is being accounted, and MAY define the concept of a multi-session. For instance, the NASREQ DIAMETER application treats a single PPP connection to a Network Access Server as one session, and a set of Multilink PPP sessions as one multi-session. 9.7. Accounting Command-Codes

This section defines Command-Code values that MUST be supported by all Diameter implementations that provide Accounting services. 9.7.1. Accounting-Request

The Accounting-Request (ACR) command, indicated by the Command-Code field set to 271 and the Command Flags’ ’R’ bit set, is sent by a Diameter node, acting as a client, in order to exchange accounting information with a peer. One of Acct-Application-Id and Vendor-Specific-Application-Id AVPs MUST be present. If the Vendor-Specific-Application-Id grouped AVP is present, it must have an Acct-Application-Id inside. The AVP listed below SHOULD include service specific accounting AVPs, as described in Section 9.3.

The Accounting-Answer (ACA) command, indicated by the Command-Code field set to 271 and the Command Flags’ ’R’ bit cleared, is used to acknowledge an Accounting-Request command. The Accounting-Answer command contains the same Session-Id and includes the usage AVPs only if CMS is in use when sending this command. Note that the inclusion of the usage AVPs when CMS is not being used leads to unnecessarily large answer messages, and can not be used as a server’s proof of the receipt of these AVPs in an end-to-end fashion. If the AccountingRequest was protected by end-to-end security, then the corresponding ACA message MUST be protected by end-to-end security. Only the target Diameter Server, known as the home Diameter Server, SHOULD respond with the Accounting-Answer command. One of Acct-Application-Id and Vendor-Specific-Application-Id AVPs MUST be present. If the Vendor-Specific-Application-Id grouped AVP is present, it must have an Acct-Application-Id inside. The AVP listed below SHOULD include service specific accounting AVPs, as described in Section 9.3.

The Accounting-Record-Type AVP (AVP Code 480) is of type Enumerated and contains the type of accounting record being sent. The following values are currently defined for the Accounting-Record-Type AVP: EVENT_RECORD 1 An Accounting Event Record is used to indicate that a one-time event has occurred (meaning that the start and end of the event are simultaneous). This record contains all information relevant to the service, and is the only record of the service. START_RECORD 2 An Accounting Start, Interim, and Stop Records are used to indicate that a service of a measurable length has been given. An Accounting Start Record is used to initiate an accounting session, and contains accounting information that is relevant to the initiation of the session.

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and so on until the session ends and a STOP_RECORD record is produced. The Value field of this AVP is the nominal interval between these records in seconds. and STOP_RECORD are produced. The omission of the Acct-Interim-Interval AVP or its inclusion with Value field set to 0 means that EVENT_RECORD. as appropriate for the service. based on the needs of the home-organization. The following accounting record production behavior is directed by the inclusion of this AVP: 1.RFC 3588
Diameter Based Protocol
September 2003
INTERIM_RECORD 3 An Interim Accounting Record contains cumulative accounting information for an existing accounting session. two. Interim Accounting Records SHOULD be sent every time a re-authentication or re-authorization occurs. service sessions can result in one. or two+N accounting records. the next one again as the interval has elapsed once more.
Calhoun. The client MUST ensure that the interim record production times are randomized so that large accounting message storms are not created either among records or around a common service start time.
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. 9. 2. known as the client. MUST produce the first INTERIM_RECORD record roughly at the time when this nominal interval has elapsed from the START_RECORD. The client uses information in this AVP to decide how and when to produce accounting records. Acct-Interim-Interval
The Acct-Interim-Interval AVP (AVP Code 85) is of type Unsigned32 and is sent from the Diameter home authorization server to the Diameter client. additional interim record triggers MAY be defined by application-specific Diameter applications.8.2. With different values in this AVP. START_RECORD. The selection of whether to use INTERIM_RECORD records is done by the Acct-Interim-Interval AVP. The inclusion of the AVP with Value field set to a non-zero value means that INTERIM_RECORD records MUST be produced between the START_RECORD and STOP_RECORD records. et al. STOP_RECORD 4 An Accounting Stop Record is sent to terminate an accounting session and contains cumulative accounting information relevant to the existing session. Further. The Diameter node that originates the accounting information.

and can be used in matching accounting records with confirmations. As Session-Id AVPs are globally unique. et al.
Accounting-Record-Number AVP
The Accounting-Record-Number AVP (AVP Code 485) is of type Unsigned32 and identifies this record within one session. and MUST be used in all accounting messages for the given session.6.8. and so on until the value for STOP_RECORD is one more than for the last INTERIM_RECORD. Accounting-Sub-Session-Id AVP
The Accounting-Sub-Session-Id AVP (AVP Code 287) is of type Unsigned64 and contains the accounting sub-session identifier.8. An easy way to produce unique numbers is to set the value to 0 for records of type EVENT_RECORD and START_RECORD. Acct-Multi-Session-Id AVP
The Acct-Multi-Session-Id AVP (AVP Code 50) is of type UTF8String. and the value of this AVP MUST be monotonically increased by one for all new sub-sessions. but the same Acct-Multi-Session-Id AVP. This AVP contains the contents of the RADIUS Acct-Session-Id attribute. 2 for the second.8.
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. Accounting-Realtime-Required AVP
The Accounting-Realtime-Required AVP (AVP Code 483) is of type Enumerated and is sent from the Diameter home authorization server to the Diameter client or in the Accounting-Answer from the accounting server. 9. following the format specified in Section 8.
Calhoun. A STOP_RECORD message with no Accounting-Sub-Session-Id AVP present will signal the termination of all sub-sessions for a given Session-Id. The client uses information in this AVP to decide what to do if the sending of accounting records to the accounting server has been temporarily prevented due to. a network problem. and set the value to 1 for the first INTERIM_RECORD.3.5. 9. for instance. the combination of Session-Id and AccountingRecord-Number AVPs is also globally unique.RFC 3588
Diameter Based Protocol
September 2003
9. 9. Acct-Session-Id AVP
The Acct-Session-Id AVP (AVP Code 44) is of type OctetString is only used when RADIUS/Diameter translation occurs.8. with the exception of an Accounting-Request whose Accounting-Record-Type is set to STOP_RECORD. This AVP MAY be returned by the Diameter server in an authorization answer. The absence of this AVP implies no sub-sessions are in use.8. 9.7. The combination of the Session-Id and this AVP MUST be unique per subsession.4. where each session would have a unique Session-Id. The Acct-MultiSession-Id AVP is used to link together multiple related accounting sessions.8.

Note that the set of alternative accounting servers are treated as one server in this sense.
Calhoun. and specifies in which Diameter messages they MAY. AVP Occurrence Table The following tables presents the AVPs defined in this document.
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.
The table in this section is limited to the non-accounting Command Codes defined in this specification. Zero or one instance of the AVP MAY be present in the message. or MAY NOT be present.RFC 3588
Diameter Based Protocol
September 2003
DELIVER_AND_GRANT 1 The AVP with Value field set to DELIVER_AND_GRANT means that the service MUST only be granted as long as there is a connection to an accounting server. It is considered an error if there are more than one instance of the AVP.4. The table uses the following symbols: 0 0+ 0-1 The AVP MUST NOT be present in the message. GRANT_AND_LOSE 3 The AVP with Value field set to GRANT_AND_LOSE means that service SHOULD be granted even if the records can not be delivered or stored.1. GRANT_AND_STORE 2 The AVP with Value field set to GRANT_AND_STORE means that service SHOULD be granted if there is a connection. Note that AVPs that can only be present within a Grouped AVP are not represented in this table. At least one instance of the AVP MUST be present in the message. One instance of the AVP MUST be present in the message. 10. This is the default behavior if the AVP isn’t included in the reply from the authorization server. Zero or more instances of the AVP MAY be present in the message. et al. Base Protocol Command AVP Table
1 1+
10. or as long as records can still be stored as described in Section 9. Having to move the accounting record stream to a backup server is not a reason to discontinue the service to the user.

1. 11. A denial notice must be justified by an explanation and. Vendor-ID and Flags field. the AVP header contains three fields that requires IANA namespace management. "Standards Action". in accordance with BCP 26 [IANA].RFC 3588
Diameter Based Protocol
September 2003
11. in the cases where it is possible. Before a period of 30 days has passed. and allocations SHOULD NOT be made for purposes unrelated to authentication. The following policies are used here with the meanings defined in BCP 26: "Private Use". Vendors can have their own AVP Codes namespace which will be identified by their Vendor-ID (also known as Enterprise-Number) and they control the assignments of their vendorspecific AVP codes within their own namespace. the request is posted to the AAA WG mailing list (or. For registration requests where a Designated Expert should be consulted. concrete suggestions on how the request can be modified so as to become acceptable.
11. For Designated Expert with Specification Required. "Specification Required". the Designated Expert will either approve or deny the registration request and publish a notice of the decision to the AAA WG mailing list or its successor. and MUST include a pointer to a public specification. the responsible IESG area director should appoint the Designated Expert. This section explains the criteria to be used by the IANA for assignment of numbers within namespaces defined within this document. a successor designated by the Area Director) for comment and review. the AVP Code. "First Come First Served".
IANA Considerations This section provides guidance to the Internet Assigned Numbers Authority (IANA) regarding registration of values related to the Diameter protocol.
Calhoun.
AVP Header
As defined in Section 4.1. The AVP Codes and sometimes also possible values in an AVP are controlled and maintained by IANA. et al. authorization or accounting. Diameter is not intended as a general purpose protocol. "IETF Consensus".1.
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. if it has been disbanded. There are multiple namespaces. The absence of a Vendor-ID or a Vendor-ID value of zero (0) identifies the IETF IANA controlled AVP Codes namespace. AVP Codes
The AVP Code namespace is used to identify attributes. "Expert Review".

AVPs may be allocated following Designated Expert with Specification Required [IANA]. See Section 3.214 and 16. This document defines the Command Codes 257.2. no guarantee is made for interoperability between Diameter peers using experimental commands.1.RFC 3588
Diameter Based Protocol
September 2003
AVP Code 0 is not used.5 for the assignment of the namespace in this specification. 291-300. and are defined as "RADIUS Packet Type Codes" in [RADTYPE]. See Section 4. Diameter Header
As defined in Section 3. where no interoperability is deemed useful. AVP Codes 1-255 are managed separately as RADIUS Attribute Types [RADTYPE]. 276-285.777. Vendor-Specific AVPs codes are for Private Use and should be encouraged instead of allocation of global attribute types. et al. 258. 280 and 282. bit 1 The remaining bits should [IANA].
There are 8 bits in the AVP Flags field Section 4.777. allocation of global AVPs should be encouraged instead. for functions specific only to one vendor’s implementation of Diameter. Where a Vendor-Specific AVP is implemented by more than one vendor. Values 25616. Command Codes
The Command Code namespace is used to identify Diameter commands. 271. only be assigned via a Standards Action 11.
Calhoun. 11. The values 16. allocated by IETF Consensus [IANA].215 (hexadecimal values 0xfffffe 0xffffff) are reserved for experimental commands. Command Code and Command Flags. 480. 274-275. standard commands. As these codes are only for experimental and testing purposes.1.1 for the assignment of the namespace in this specification.2. 483 and 485-486. AVP Flags of the AVP header. Release of blocks of AVPs (more than 3 at a time for a given purpose) should require IETF Consensus. Note that Diameter defines a mechanism for Vendor-Specific AVPs. This document defines the AVP Codes 257-274.
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. 11.2. This document assigns bit 0 (’M’andatory) and bit 2 (’P’rotected).213 are for permanent.777. the Diameter header contains two fields that require IANA namespace management. 287. as outlined in [IANA-EXP]. defined in (’V’endor Specific). where the Vendor-Id field in the AVP header is set to a non-zero value. The values 0-255 are reserved for RADIUS backward compatibility.

4. The following values are allocated.0xfffffffe for vendor specific applications. Both Application-Id and Acct-Application-Id AVPs use the same Application Identifier space.2. 4001-4002 and 5001-5017. et al. adding additional values to the list can be done on a First Come. This document assigns bit 0 (’R’equest).4. There are standards-track application ids and vendor specific application ids.RFC 3588
Diameter Based Protocol
September 2003
11. are for Private Use. 11. bit 1 (’P’roxy).
Command Flags
There are eight bits in the Command Flags field of the Diameter header.2.
Calhoun.4. First Served basis by IANA.3.1.
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. and 0x01000000 . AVP Values
Certain AVPs in Diameter define a list of values with various meanings. 2001-2002. Bits 4 through 7 MUST only be assigned via a Standards Action [IANA]. Vendor-Specific Application Identifiers. 11. the Application Identifier is used to identify a specific Diameter Application. IANA [IANA] has assigned the range 0x00000001 to 0x00ffffff for standards-track applications. First Served basis by IANA. Result-Code AVP Values
As defined in Section 7. For attributes other than those specified in this section. bit 2 (’E’rror) and bit 3 (’T’). All remaining values are available for assignment via IETF Consensus [IANA]. Application Identifiers
As defined in Section 2.1. first-served basis. the Result-Code AVP (AVP Code 268) defines the values 1001. Diameter Common Messages NASREQ Mobile-IP Diameter Base Accounting Relay 0 1 [NASREQ] 2 [DIAMMIP] 3 0xffffffff
Assignment of standards-track application IDs are by Designated Expert with Specification Required [IANA]. Vendor-Specific Application Identifiers are assigned on a First Come. 3001-3010. 11. on a first-come.

The following values have been placed into the registry: Services Field AAA+D2T AAA+D2S 12.4.8. the Inband-Security-Id AVP (AVP Code 299) defines the values 0-1.4.12.12. 11. 11. Name and Contact Information: The name. This MUST include the name and acronym for the protocol. Protocol TCP SCTP
Diameter protocol related configurable parameters This section contains the configurable parameters that are found throughout this document:
Calhoun.5. All remaining values are available for assignment via IETF Consensus [IANA].RFC 3588
Diameter Based Protocol
September 2003
11. the Re-Auth-Request-Type AVP (AVP Code 285) defines the values 0-1. 11. Protocol: The specific transport protocol associated with that service field. email address and telephone number for the person performing the registration. Inband-Security-Id AVP (code 299)
As defined in Section 6. RFC 5766". address. An example for a new fictitious transport protocol called NCTP might be "AAA+D2N". NAPTR Service Fields
The registration in the RFC MUST include the following information: Service Field: The service field being registered. Accounting-Realtime-Required AVP Values
As defined in Section 9. along with reference to a document that describes the transport protocol. All remaining values are available for assignment via IETF Consensus [IANA].
Re-Auth-Request-Type AVP Values
As defined in Section 8. the Accounting-Realtime-Required AVP (AVP Code 483) defines the values 1-3.10. Diameter TCP/SCTP Port Numbers
The IANA has assigned TCP and SCTP port number 3868 to Diameter. All remaining values are available for assignment via IETF Consensus [IANA].11.6.7."New Connectionless Transport Protocol (NCTP).
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. For example . 11. et al.4.10.

end-to-end security is needed. Diameter clients. Security Considerations The Diameter base protocol assumes that messages are secured by using either IPSec or TLS.
Calhoun. 13. It is suggested that IPsec be used primarily at the edges for intradomain exchanges.RFC 3588
Diameter Based Protocol
September 2003
Diameter Peer A Diameter entity MAY communicate with peers that are statically configured. which is typically used for all messages that cannot be locally processed. a TLS handshake will begin when both ends are in the open state. TLS is recommended. both ends move to the closed state. The server MUST have a table of Realm Names.1 and 13. et al. If a Diameter connection is not protected by IPsec. For NAS devices without certificate support. The routing table MAY also include a "default route". then the CER/CEA exchange MUST include an Inband-Security-ID AVP with a value of TLS. Realm Routing Table A Diameter proxy server routes messages based on the realm portion of a Network Access Identifier (NAI). after completion of the CER/CEA exchange. all further messages will be sent via TLS. In other situations. Diameter implementations MUST use transmission-level security of some kind (IPsec or TLS) on each connection. A statically configured Diameter peer would require that either the IP address or the fully qualified domain name (FQDN) be supplied. For TLS usage. The recommended value is 30 seconds.2 for more details on IPsec and TLS usage. preshared keys can be used between the NAS and a local AAA proxy. Diameter servers MUST support TLS and IPsec. If the handshake fails. If the TLS handshake is successful. Tc timer The Tc timer controls the frequency that transport connection attempts are done to a peer with whom no active transport connection exists. This security mechanism is acceptable in environments where there is no untrusted third party agent. and the address of the peer to which the message must be forwarded to. See Sections 13. which would then be used to resolve through DNS.
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. such as Network Access Servers (NASes) and Mobility Agents MUST support IP Security [SECARCH] and MAY support TLS [TLS]. For protection of inter-domain exchanges.

However. and key management. when used in conformant implementations. and MUST support the replay protection mechanisms of IPsec. Peer authentication using the public key encryption methods outlined in IKE’s Sections 5. integrity protection and confidentiality. and IKE Main Mode SHOULD NOT be used.
Calhoun.2 and 5.RFC 3588
Diameter Based Protocol
September 2003
13. it is preferable to leave the connection up. Conformant implementations MUST support both IKE Main Mode and Aggressive Mode. When digital signatures are used to achieve authentication.
IPsec Usage
All Diameter implementations MUST support IPsec ESP [IPsec] in transport mode with non-null encryption and authentication algorithms to provide per-packet authentication. negotiation of security associations. et al. This avoids the potential for continually bringing connections up and down. The receipt of an IKE Phase 2 delete message SHOULD NOT be interpreted as a reason for tearing down a Diameter connection. using the IPsec DOI [IPSECDOI].1. and if additional traffic is sent on it. and MAY support certificatebased peer authentication using digital signatures.3 [IKE] SHOULD NOT be used. The Phase 2 Quick Mode exchanges used to negotiate protection for Diameter connections MUST explicitly carry the Identity Payload fields (IDci and IDcr). When digital signatures are used for authentication. either IKE Main Mode or IKE Aggressive Mode MAY be used. When pre-shared keys are used for authentication. IKE negotiators SHOULD use pertinent certificate revocation checks before accepting a PKI certificate for use in IKE’s authentication procedures. This allows the Phase 2 security association to correspond to specific TCP and SCTP connections. Diameter implementations MUST support peer authentication using a pre-shared key. each ID Payload MUST carry a single IP address and a single non-zero port number. an IKE negotiator SHOULD use IKE Certificate Request Payload(s) to specify the certificate authority (or authorities) that are trusted in accordance with its local policy. Diameter implementations MUST support IKE for peer authentication. Since IPsec acceleration hardware may only be able to handle a limited number of active IKE Phase 2 SAs. and MUST NOT use the IP Subnet or IP Address Range formats. IKE Aggressive Mode SHOULD be used. as a means of keeping the number of active Phase 2 SAs to a minimum. to bring up another IKE Phase 2 SA to protect it. Rather. The DOI provides for several types of identification data. Phase 2 delete messages may be sent for idle SAs.
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.

RFC 3588
Diameter Based Protocol
September 2003
13.2. it is necessary to configure the root certificate authorities trusted by the Diameter peer. In general. it is expected that those root CAs will be configured so as to reflect the business relationships between the organization hosting the Diameter peer and other organizations. When certificate authentication Diameter peers may not be known beforehand.3. and therefore peer discovery may be required. Diameter nodes MUST be able to negotiate the following TLS cipher suites: TLS_RSA_WITH_RC4_128_MD5 TLS_RSA_WITH_RC4_128_SHA TLS_RSA_WITH_3DES_EDE_CBC_SHA Diameter nodes SHOULD be able to negotiate the following TLS cipher suite: TLS_RSA_WITH_AES_128_CBC_SHA Diameter nodes MAY negotiate other TLS cipher suites. When certificates are used. proper configuration of the trust model within a Diameter peer is essential to security. et al.
TLS Usage
A Diameter node that initiates a connection to another Diameter node acts as a TLS client according to [TLS].
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. and the Diameter node acting as TLS client MUST be prepared to supply a certificate on request. In order to ensure mutual authentication. a Diameter peer will typically not be configured to allow connectivity with any arbitrary peer. These root CAs are likely to be unique to Diameter usage and distinct from the root CAs that might be trusted for other purposes such as Web browsing. the Diameter node acting as TLS server must request a certificate from the Diameter node acting as TLS client. As a result. within IPsec it is not possible to uniquely configure trusted root CAs for each application individually. This implies. 13. Note that IPsec is considerably less flexible than TLS when it comes to configuring root CAs. the same policy must be used for all applications. Diameter nodes implementing TLS for security MUST mutually authenticate as part of TLS session establishment. Since use of Port identifiers is prohibited within IKE Phase 1. and a Diameter node that accepts a connection acts as a TLS server. for example. Peer-to-Peer Considerations
As with any peer-to-peer protocol. that a root CA trusted for use with Diameter must also be
Calhoun.

Calhoun. use of a simple static policy is the often the simplest route to IPsec-enabling a Diameter implementation. but not both. When IPsec is used with Diameter.. the policy would be "Require IPsec. who are identified by their IP address (Main Mode). from any to me. and to be required whenever an inbound Diameter connection occurs. unique pre-shared keys are configured with Diameter peers. As a result. This policy is attractive. without reserving an additional port for TLS usage.g. for inbound traffic. Inconsistent use of security mechanisms can result in redundant security mechanisms being used (e. IPsec is most appropriate for intra-domain usage when pre-shared keys are used as a security mechanism. Therefore. it would be necessary to plumb peer-specific policies either statically or dynamically. This policy causes IPsec to be used whenever a Diameter peer initiates a connection to another Diameter peer. The following is intended to provide some guidance on the issue. an IPsec SA is automatically created based on a simple static policy. it is necessary for the set of Diameter peers to be known beforehand. peer discovery is typically not necessary. TLS over IPsec) or worse. TLS SHOULD be used to protect Diameter connections between administrative domains. a typical security policy for outbound traffic is "Initiate IPsec.
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. To avoid this. and both IPsec and TLS will be used to protect the Diameter connection. It is recommended that a Diameter peer implement the same security mechanism (IPsec or TLS) across all its peer-to-peer connections. potential security vulnerabilities. and IPsec policy functionality is implementation dependent. Since TLS supports application-level granularity in certificate policy. These restrictions can be awkward at best. since it does not require policy to be set for each peer or dynamically modified each time a new Diameter connection is created. or possibly their FQDN (Aggressive Mode). et al.RFC 3588
Diameter Based Protocol
September 2003
trusted to protect SNMP. When pre-shared key authentication is used with IPsec to protect Diameter. where the recommended IPsec policy is put in place. there is not a convenient way in which to use either TLS or IPsec. One implication of the recommended policy is that if a node is using both TLS and IPsec. Since Diameter uses the same port for TLS and non-TLS usage. Since IPsec extensions are typically not available to the sockets API on most platforms. from me to any. a TLS-protected connection will match the IPsec policy. destination port Diameter". destination port Diameter".

John Schnizlein. Jonathan Wood and Bernard Aboba provided invaluable assistance in working out transport issues. The authors would also like to acknowledge the following people for their contribution in the development of the Diameter protocol: Allan C. Ryan Moats.
Calhoun. Paul Funk and David Mitton were instrumental in getting the Peer State Machine correct. Jacques Caron provided many great comments as a result of a thorough review of the spec. November 1998. Kenneth Peirce.
[TACACS]
15. et al.
Acknowledgements The authors would like to thank Nenad Trifunovic. William Bulley. Finally. "An Access Control Protocol. Daniel C. Victor Muslin. Finseth. Mark Jones and Dave Spence. Stephen Farrell. Rubens. Mark Eklund.RFC 3588
Diameter Based Protocol
September 2003
[SECARCH]
Kent.
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. Allison Mankin. Pat Calhoun would like to thank Sun Microsystems since most of the effort put into this document was done while he was in their employ. Haseeb Akhtar. David Frascone. RFC 1492. Fox. Bob Kopacz. Vollbrecht and Jeff Weisberg. Nancy Greene. Text in this document was also provided by Paul Funk. Fredrik Johansson. Peter Heitman. C. Mark Jones. "Security Architecture for the Internet Protocol".. S. Paul Krumviede. July 1993. and our deep thanks go to them for their time. Ignacio Goyret. Sometimes Called TACACS". and R. Atkinson. Lol Grant. Fergal Ladley. Tony Johansson and Pankaj Patel for their participation in the pre-IETF Document Reading Party. and similarly with Steven Bellovin in the security area. John R. Martin Julien. RFC 2401. Sumit Vakil.

# . Additional applications may be defined in the future.Guttman@sun.com> Language of service template: en Security Considerations: Diameter clients and servers use various cryptographic mechanisms to protect communication integrity. as Diameter services are vital for network operation it is important to use SLPv2 authentication to prevent an attacker from modifying or eliminating service advertisements for legitimate Diameter servers. confidentiality as well as perform end-point authentication.9.
Diameter Service Template
The following service template describes the attributes used by Diameter servers to advertise themselves. an AAA server to use for accounting. . Template text: -------------------------template begins here----------------------template-type=service:diameter template-version=0. Diameter implementations support one or more applications.0 template-description= The Diameter protocol is defined by RFC 3588. A Diameter client can request specific Diameter servers based on characteristics of the Diameter service desired (for example.) Name of submitter: "Erik Guttman" <Erik. template-url-syntax= url-path= . It would thus be difficult if not impossible for an attacker to advertise itself using SLPv2 and pose as a legitimate Diameter peer without proper preconfigured secrets or cryptographic keys.com:1812. This simplifies the process of selecting an appropriate server to communicate with.RFC 3588
Diameter Based Protocol
September 2003
Appendix A. Still.
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.example. Example: ’aaa://aaa.
Calhoun.transport=tcp supported-auth-applications= string L M # This attribute lists the Diameter applications supported by the # AAA implementation. # An updated service template will be created at that time. et al. The Diameter URL format is described in Section 2. The applications currently defined are: # Application Name Defined by # -------------------------------------------------# NASREQ Diameter Network Access Server Application # MobileIP Diameter Mobile IP Application # # Notes: # .

ex. Priority Weight Port Target IN SRV 0 1 5060 server1.example. though it MAY support other # transports. # An updated service template will be created at that time. # NASREQ. SCTP will be used.example. Diameter implementations support one or more applications._tcp.. order pref flags service IN NAPTR 50 50 "s" "AAA+D2S" _diameter.example. If the client supports over SCTP.MobileIP supported-acct-applications= string L M # This attribute lists the Diameter applications supported by the # AAA implementation. SCTP.com.com IN NAPTR 100 "" _aaa.com IN SRV 2 5060 server2. # .example._sctp. and the following NAPTR records are returned: . Additional applications may be defined in the future.TCP -------------------------template ends here----------------------Appendix B. That lookup would return: .. et al. and TCP. targeted to a host determined by an SRV lookup of _diameter. Note that a compliant Diameter # implementation MUST support SCTP.RFC 3588
Diameter Based Protocol
September 2003
# NASREQ. too.com regexp replacement "" 50 "s" "AAA+D2T"
This indicates that the server supports SCTP.com
0
Calhoun. NAPTR Example
As an example.com.MobileIP supported-transports= string L M SCTP # This attribute lists the supported transports that the Diameter # implementation accepts. in that order._sctp.
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. consider a client that wishes to resolve aaa:ex. The applications currently defined are: # Application Name Defined by # -------------------------------------------------# NASREQ Diameter Network Access Server Application # MobileIP Diameter Mobile IP Application # # Notes: # . The client performs a NAPTR query for that domain.

servers that do this MUST ensure that duplicates are found even when the first transmitted request arrives at the server after the retransmitted request. due to failover to an alternate server. Implementation problems and misconfiguration. after a reboot. due to a recovered primary peer or due to a client re-sending a stored record from non-volatile memory such as after reboot of a client or agent). For instance.
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. At that time records are likely to be sorted according to the included User-Name and duplicate elimination is easy in this case.. the likelihood of duplication will vary according to the implementation.
-
-
-
The T flag is used as an indication of an application layer retransmission event. This will result in retransmission of the record soon after the client or agent has rebooted.
Duplicate Detection
As described in Section 9.g. Failure of a client or agent after sending of a record from nonvolatile memory. In other situations it may be necessary to perform real-time duplicate detection. In some cases the Diameter accounting server can delay the duplicate detection and accounting record processing until a post-processing phase takes place. Duplicates received from RADIUS gateways.RFC 3588
Diameter Based Protocol
September 2003
Appendix C.g. (e. such as when credit limits are imposed or real-time fraud detection is desired.4. e. Where close to real-time performance is required. It can be used only in cases where no answer has been received from the Server for a request and the request is sent again. due to a failover to an alternate peer. a client may not know whether it has already tried to send the accounting records in its nonvolatile memory before the reboot occurred. but prior to receipt of an application layer ACK and deletion of the record. record to be sent. failover thresholds need to be kept low and this may lead to an increased likelihood of duplicates.. However.
Calhoun. accounting record duplicate detection is based on session identifiers. et al. Since the retransmission behavior of RADIUS is not defined within [RFC2865]. Failover can occur at the client or within Diameter agents. Diameter servers MAY use the T flag as an aid when processing requests and detecting duplicate messages. It is defined only for request messages sent by Diameter clients or agents. Duplicates can appear for various reasons: Failover to an alternate server.

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. so this approach represents a substantial optimization of the duplicate detection process. it is possible for the original record to be received after the T flag marked record. For example. This limits database searching to those records where the T flag is set. if sent. In order to be able to detect out of order duplicates. Since the T flag does not affect interoperability. the Diameter server can delay processing records with the T flag set until a time period TIME_WAIT + RECORD_PROCESSING_TIME has elapsed after the closing of the original transport connection. it can choose to make use of the T flag or not. After this time period has expired. If the T flag is set in the request message. in order to optimize duplicate detection. the server searches for a duplicate within a configurable duplication time window backward and forward. have been received and recorded. hashing techniques or other schemes. As an example. generation of the T flag is REQUIRED for Diameter clients and agents. A Diameter server MAY check the T flag of the received message to determine if the record is a possible duplicate. it can be usually be assumed that duplicates appear within a time window of longest recorded network partition or device fault. but MAY be implemented by Diameter servers.
Calhoun. The following is an example of how the T flag may be used by the server to detect duplicate requests. due to differences in network delays experienced along the path by the original and duplicate transmissions. During failover. such as the use of the T flag in the received messages. network partitions and device faults will presumably be rare events. Since the Diameter server is responsible for duplicate detection. In a well run network. only generation of duplicates due to failover or resending of records in non-volatile storage can be reliably detected by Diameter clients or agents. So only records within this time window need to be looked at in the backward direction. Secondly. perhaps a day. et al. may be used to eliminate the need to do a full search even in this set except for rare cases. the Diameter server should use backward and forward time windows when performing duplicate checking for the T flag marked request. The likelihood of this occurring increases as the failover interval is decreased. In such cases the Diameter client or agents can mark the message as possible duplicate by setting the T flag. and may not be needed by some servers. in order to allow time for the original record to exit the network and be recorded by the accounting server. then it may check the T flag marked records against the database with relative assurance that the original records.RFC 3588
Diameter Based Protocol
September 2003
In general.

or other proprietary rights which may cover technology that may be required to practice this standard. neither does it represent that it has made any effort to identify any such rights. Please address the information to the IETF Executive Director. patents or patent applications.
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. et al.
Calhoun.RFC 3588
Diameter Based Protocol
September 2003
Appendix D.
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available. The IETF invites any interested party to bring to its attention any copyrights. Copies of claims of rights made available for publication and any assurances of licenses to be made available. or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF Secretariat. Information on the IETF’s procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11.

This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES. published and distributed. in whole or in part. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. copied. or as required to translate it into languages other than English. and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared. et al. provided that the above copyright notice and this paragraph are included on all such copies and derivative works.RFC 3588
Diameter Based Protocol
September 2003
Full Copyright Statement Copyright (C) The Internet Society (2003). However.
Calhoun. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society.
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. except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed. INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. this document itself may not be modified in any way.
This document and translations of it may be copied and furnished to others. such as by removing the copyright notice or references to the Internet Society or other Internet organizations. EXPRESS OR IMPLIED. All Rights Reserved. without restriction of any kind.